Is Samma Dithi Right understanding or Right view?

It does not matter what word we use even though I tend to like the term "right view". You are forming views when you do not know something for sure so the best bet is to have the right view. Buddha enumerated 62 kinds of views. So if you read Brahamjala Sutta you can decide yourself what is the best terminology for this understanding.

https://www.dhammatalks.org/suttas/DN/DN01.html

"(view) position", "(view) point", "stand", "taking right stand", might be usefull to understand "Diṭṭhi", good householder.

And what is "taking on a proper stand", to cultivate toward higher and liberation:

"And how is one made pure in three ways by mental action? There is the case where a certain person is not covetous. He does not covet the belongings of others, thinking, 'O, that what belongs to others would be mine!' He bears no ill will and is not corrupt in the resolves of his heart. [He thinks,] 'May these beings be free from animosity, free from oppression, free from trouble, and may they look after themselves with ease!' He has right view and is not warped in the way he sees things: 'There is what is given, what is offered, what is sacrificed. There are fruits & results of good & bad actions. There is this world & the next world. There is mother & father. There are spontaneously reborn beings; there are brahmans & contemplatives who, faring rightly & practicing rightly, proclaim this world & the next after having directly known & realized it for themselves.' This is how one is made pure in three ways by mental action."
— AN 10.176

The safe bet may help to cut down inner arguments against this proper stand, increasing gratitude.

[That's not given for stacks, exchange, other world-binding trades, but for an escape from this wheel]

Diṭṭhi in Pali literally means "sight", but here it is used to mean view, belief, dogma, theory, speculation.

Sammā diṭṭhi means Right View.

There are many other words in the PTS Pali-English Dictionary which may be used for "understanding" in different contexts, but diṭṭhi is not one of them.

From PTS Pali-English Dictionary on Diṭṭhi:

Diṭṭhi Diṭṭhi (f.) [Sk. dṛṣṭi; cp. dassana] view, belief, dogma, theory, speculation, esp. false theory, groundless or unfounded opinion.

From Pali Kanon: Manual of Buddhist Terms and Doctrines:

(lit. 'sight'; Ö dis, to see): view, belief, speculative opinion, insight.

If not qualified by sammā, 'right', it mostly refers to wrong and evil view or opinion, and only in a few instances to right view, understanding or insight (e.g. ditthi-ppatta, q.v.; ditthi-visuddhi, purification of insight; ditthi-sampanna, possessed of insight).

Wrong or evil views (ditthi or micchā-ditthi) are declared as utterly rejectable for being a source of wrong and evil aspirations and conduct, and liable at times to lead man to the deepest abysses of depravity, as it is said in A. I, 22:

"No other thing than evil views do I know, o monks, whereby to such an extent the unwholesome things not yet arisen arise, and the unwholesome things already arisen are brought to growth and fullness. No other thing than evil views do I know, whereby to such an extent the wholesome things not yet arisen are hindered in their arising, and the wholesome things already arisen disappear. No other thing than evil views do I know, whereby to such an extent human beings at the dissolution of the body, at death, are passing to a way of suffering, into a world of woe, into hell." Further in A. I, 23: "Whatever a man filled with evil views performs or undertakes, or whatever he possesses of will, aspiration, longing and tendencies, all these things lead him to an undesirable, unpleasant and disagreeable state, to woe and suffering."

From the Abhidhamma (Dhs) it may be inferred that evil views, whenever they arise, are associated with greed (s. Tab. I. 22, 23, 26, 27).

Numerous speculative opinions and theories, which at all times have influenced and still are influencing mankind, are quoted in the sutta-texts. Amongst them, however, the wrong view which everywhere, and at all times, has most misled and deluded mankind is the personality-belief, the ego-illusion. This personality-belief (sakkāya-ditthi), or ego-illusion (atta-ditthi), is of 2 kinds: eternity-belief and annihilation-belief.

Eternity-belief (sassata-ditthi) is the belief in the existence of a persisting ego-entity, soul or personality, existing independently of those physical and mental processes that constitute life and continuing even after death.

Annihilation-belief (uccheda-ditthi), on the other hand, is the belief in the existence of an ego-entity or personality as being more or less identical with those physical and mental processes, and which therefore, at the dissolution at death, will come to be annihilated. - For the 20 kinds of personality-belief, see sakkāya-ditthi.

Now, the Buddha neither teaches a personality which will continue after death, nor does he teach a personality which will be annihilated at death, but he shows us that 'personality', 'ego', 'individual', 'man', etc., are nothing but mere conventional designations (vohāra-vacana) and that in the ultimate sense (s. paramattha-sacca) there is only this self-consuming process of physical and mental phenomena which continually arise and again disappear immediately.

"The Perfect One is free from any theory (ditthigata), for the Perfect One has seen what corporeality is, and how it arises and passes away. He has seen what feeling ... perception ... mental formations ... consciousness are, and how they arise and pass away. Therefore I say that the Perfect One has won complete deliverance through the extinction, fading away, disappearance, rejection and casting out of all imaginings and conjectures, of all inclination to the 'vain-glory of 'I' and 'mine." (M. 72).