What is the most accurate translation of the word 'dukkha'?

'Dukkha' = du + kha = 'hard/difficult to endure' or 'unbearable'

In its most basic ordinary unenlightened sense, 'dukkha' refers to physical pain and painful feelings, such as grief & sorrow, which in the Pali is called 'dukkha vedana' or 'painful feelings'. For most people, such feelings are 'difficult to endure' or 'unbearable'.

In its enlightened sense, 'dukkha' has two aspects, namely:

1. The mental turmoil or torment of attachment, self-obsession or selfishness, called 'upadana dukkha', where in the 1st noble truth, the Buddha summarised all dukkha as attachment (upadana) to the five aggregates. This is mostly simply explained in the sutta SN 22.1. Many others sutta, such as the well-known SN 36.6, similarly make it clear real dukkha is attachment, which includes attachment to physical pain. Therefore, the revelation of the Buddha was dukkha was attachment rather than physical pain, sorrow, sickness, death, etc. In other words, sorrow, sickness and death are forms of attachment, namely, the ideas "I am sick; I am getting old; I will die; my friend died". In Buddhism, 'death' occurs to a 'self', which is why death does not happen to a Buddha because a Buddha does not believe they are a 'self'.

2. Dukkha as the 'lack of pleasantness' or 'non-pleasurableness' or 'unsatisfactoriness' in conditioned impermanent phenomena, as taught in SN 22.59. In lucid meditation when impermanence is experienced very clearly, the constant impermanence of phenomena has an unpleasant, ugly &/or disillusioning appearance. This is also called 'dukkha' however this type of dukkha is not suffering but, instead, is the vehicle for enlightenment and ending suffering, as described in Dhp 278 below:

278. "All conditioned things are unsatisfactory (dukkha)" — when one sees this with wisdom, one turns away from suffering (dukkha). This is the path to purification.

In other words, a Buddha or enlightened being is always experiencing the dukkha of impermanent phenomena but never experiences the 'upadana dukkha' of attachment. Buddhas also experience physical pain but this is merely painful feelings for a Buddha rather than suffering. Note: From an enlightened perspective, the unpleasant feelings of sorrow & grief, although being feelings, are caused by attachment and are thus types of attachment.

In conclusion, there is no precise meaning of the word "dukkha". Instead:

1. Dukkha means 'unpleasant' or 'painful' when describing a type of feeling (vedana).

2. Dukkha means 'suffering' when referring to the neurosis and torment of selfish attachment.

3. Dukkha means 'lacking happiness' or 'unsatisfactoriness' when referring to the inherent nature of impermanent phenomena. For example, a rock is 'dukkha' here because a rock has no quality in it that can sustain permanent happiness.

I think the closest fit to dukkha in English is the word 'discontent'. The essential idea behind dukkha is a mismatch between what is and what ought to be. To use the classic examples, we think we should have been born into a better condition; we think we should always be healthy; we think we should always be young and vital; we think we should live forever... The fact that we are born into our state, that we get ill, and age, and die, are dukkha because they don't fit with what we expect. We become discontent with what we've been given; we feel we should have been given something else (something better), and struggle with frustration because it isn't so.

I bow to the scholarly answers given by MAGA2020 and ruben2020 above, but I thought something more philosophical might be in order.

As i understand it Dukkha can be derived from the Sanskrit kha, one meaning of which is some sort of opening, ie 'the axle-hole of a wheel', and the antithetic prefix Duk. Meaning that if you were given a wheel to try for a fit and having tried putting it on your chariot axle you would see that the wheel's 'kha' is a bad fit. Someone would then ask you if the wheel is sukha and you would reply; no it's dukkha. So here it's close to unfitting, bad, wrong, incompatible, unsuitable, disagreeable and ill-fitting or of the wrong kind.

Sukha would be the opppsite kind of fit. Well-fitting.

I think the ill or the illness are also good translations for dukkha .

From wikipedia

According to Monier-Williams (1964), the etymology of sukha is "said to be su ['good'] + kha ['aperture'] and to mean originally 'having a good axle-hole'...." Thus, for instance, in the Rig Veda sukha denotes "running swiftly or easily" (applied, e.g., to chariots). Sukha is juxtaposed with duḥkha (Sanskrit; Pali: dukkha; often translated as "suffering"), which was established as the major motivating life principles in early Vedic religion.

In the pali we can see this applied to feelings [vedana] denoting pain as 'dukkha vedana' but it's use is broad.

There is a sutta called Dukkha which illustrates this;

"Monks, there are these three kinds of suffering.[1] What three? Suffering caused by pain,[2] suffering caused by the formations (or conditioned existence),[3] suffering due to change.[4] It is for the full comprehension, clear understanding, ending and abandonment of these three forms of suffering that the Noble Eightfold Path is to be cultivated..."

Translator's Notes (Thanissaro)

• 1. Dukkhataa, an abstract noun denoting "suffering" in the most general sense.
• 2. Dukkha-dukkhataa, the actual feeling of physical or mental pain or anguish.
• 3. Sankhaara-dukkhataa, the suffering produced by all "conditioned phenomena" (i.e., sankhaaras, in the most general sense: see BD [Buddhist Dictionary (2nd ed.), by Ven. Nyaa.natiloka, Ven. Nyaa.naponika (ed.), Colombo 1972] s.v. sankhaara I, 4). This includes also experiences associated with hedonically neutral feeling. The suffering inherent in the formations has its roots in the imperfectability of all conditioned existence, and in the fact that there cannot be any final satisfaction within the incessant turning of the Wheel of Life. The neutral feeling associated with this type of suffering is especially the indifference of those who do not understand the fact of suffering and are not moved by it.
• 4. Viparinaama-dukkhataa, the suffering associated with pleasant bodily and mental feelings: "because they are the cause for the arising of pain when they change" (VM XIV, 35).

I think that in regards to #3 It's noteworthy that it's said; 'sabbe sankhara dukkha' [all formations are dukkha] in the texts. So i think the translator made a slip there writing 'suffering produced by sankhara' and that it should be suffering associated with or suffering denoting all formations [sankhara-dukkha].

All formations are inconstant and to that extent they are flawed in as far as happiness goes, what is flawed that is classed categorically as dukkha.

I'm not sure who wrote the short introduction at the top of the Dukkha page of AccessToInsight.org but it is a very appropriate comment to your question:

No single English word adequately captures the full depth, range, and subtlety of the crucial Pali term dukkha. Over the years, many translations of the word have been used ("stress," "unsatisfactoriness," "suffering," etc.). Each has its own merits in a given context. There is value in not letting oneself get too comfortable with any one particular translation of the word, since the entire thrust of Buddhist practice is the broadening and deepening of one's understanding of dukkha until its roots are finally exposed and eradicated once and for all. One helpful rule of thumb: as soon as you think you've found the single best translation for the word, think again: for no matter how you describe dukkha, it's always deeper, subtler, and more unsatisfactory than that.

You must remember that this is a technical term that goes beyond the ordinary meaning of the word in Pali.

The canonical definition is:

"Birth is dukkha, aging is dukkha, death is dukkha; sorrow, lamentation, pain, grief, & despair are dukkha; association with the unbeloved is dukkha; separation from the loved is dukkha; not getting what is wanted is dukkha. In short, the five clinging-aggregates are dukkha."

— SN 56.11

That's quite self-explanatory. But if you want a further explanation, just look at the Dukkha page for Ven. Sariputta's elaboration.

Ven. Bodhi's comments from the forum on Understanding Dukkha:

In the Pali suttas, the discourses of the Buddha, the word dukkha is used in at least three senses. One, which is probably the original sense of the word dukkha and was used in conventional discourse during the Buddha’s time, is pain, particularly painful bodily feelings. The Buddha also uses the word dukkha for the emotional aspect of human existence. There are a number of synonyms that comprise this aspect of dukkha: soka, which means sorrow; aryadeva, which is lamentation; dolmenasa, which is sadness, grief, or displeasure; and upayasa, which is misery, even despair. The deepest, most comprehensive aspect of dukkha is signified by the term samkara-dukkha, which means the dukkha that is inherent in all conditioned phenomena simply by virtue of the fact that they are conditioned.

This means that the technical term dukkha has a superficial meaning which is pain, suffering, stress, lamentation, sorrow, grief, despair, anguish, dissatisfaction, encountering that which is disliked, being separated from that which is liked, and not getting something you want.

However, the technical term dukkha also has a deeper meaning in sankhara-dukkha - which is that all conditioned phenomena are impermanent, and therefore is a cause of suffering, because "they cannot provide stable happiness and security" (see below). It is for this reason that some people say "unsatisfactoriness" is a better term to use than "suffering" to explain the deeper meaning.

The superficial meaning covers only the negative experiences, while the deeper meaning covers the fact that positive and neutral experiences cannot be sustained forever, and negative experiences cannot be avoided forever.

In "Anicca Vata Sankhara", Ven. Bodhi comments:

The most important fact to understand about sankharas, as conditioned formations, is that they are all impermanent: "Impermanent, alas, are formations." They are impermanent not only in the sense that in their gross manifestations they will eventually come to an end, but even more pointedly because at the subtle, subliminal level they are constantly undergoing rise and fall, forever coming into being and then, in a split second, breaking up and perishing: "Their very nature is to arise and vanish." For this reason the Buddha declares that all sankharas are suffering (sabbe sankhara dukkha) — suffering, however, not because they are all actually painful and stressful, but because they are stamped with the mark of transience. "Having arisen they then cease," and because they all cease they cannot provide stable happiness and security.

To win complete release from suffering — not only from experiencing suffering, but from the unsatisfactoriness intrinsic to all conditioned existence — we must gain release from sankharas. And what lies beyond the sankharas is that which is not constructed, not put together, not compounded. This is Nibbana, accordingly called the Unconditioned — asankhata — the opposite of what is sankhata, a word which is the passive participle corresponding to sankhara. Nibbana is called the Unconditioned precisely because it's a state that is neither itself a sankhara nor constructed by sankharas; a state described as visankhara, "devoid of formations," and as sabbasankhara-samatha, "the stilling of all formations."