al-Tīn 95:2

Wa ṭūri sīnīn "By Mount Sīnīn."

It means "mountain"; but it is not a word native to Arabic. The majority of the lexicographers accept that the word comes from the Syriac/Aramaic ṭūr (mountain). In the Qurʾān this word is used almost always for one particular mountain, the mountain on which Moses received revelation.

That a word of foreign origin should be used precisely for the mountain of a foreign prophet is worth noticing. In relating an event outside the Arab country, the Qurʾān takes that country's own word.

There is a question of grammar and of reading here.

The Qurʾān names the same mountain elsewhere in a different form:

"A tree that comes forth from Mount Sīnāʾ, bringing forth oil and a relish for those who eat…" (al-Muʾminūn 23/20)

There طور سيناء (Ṭūri Sīnāʾ), here طور سينين (Ṭūri Sīnīn). The same place, two different forms.

There are two explanations for this, and they do not exclude one another:

The first — two forms in the language. The word came into Arabic from outside, and it is usual for proper names of foreign origin to acquire more than one pronunciation in Arabic. The classical lexicographers record several ways of saying such names.

The second — the requirement of the verse-ending (rhyme). Every verse of the sūra ends in the pattern -īn / -īm: zaytūn, sīnīn, amīn, taqwīm, sāfilīn, mamnūn, dīn, ḥākimīn. A long vowel followed by a nasal nūn or mīm. A sound unbroken across eight verses. The form Sīnāʾ would not enter this series; Sīnīn does.

This second explanation shows the importance the Qurʾān gives to its order of sound. But this has to be added as well: the meaning does not change for the sake of the sound — the mountain meant is the same mountain, and only one of the two forms of its name recorded in Arabic is being used.

What the word Sīnīn means has been debated separately: senses such as "blessed", "wooded", "beautiful" are transmitted. These explanations do not agree with one another and none of them is certain. The word is in all likelihood not an Arabic adjective but a part of a place name; it is not necessary to look for a meaning.

Sinai is, in the Qurʾān's narrative, the place where revelation was given directly. Moses was called there, was made to speak there, received the tablets there. The Qurʾān makes this mountain the subject of an oath in another sūra as well (Sūrat al-Ṭūr 52/1).

That a mountain should be named as a centre of revelation is the most concrete datum strengthening the place reading of the series: Ṭūr is not a fruit and cannot be; and it is identified beyond dispute with a prophet. In the middle of the series, that is, stands a "place of revelation" that nobody disputes.