Tolkien used the word Q. ve for “as, like” in Quenya for much of his life, but its etymological origins varied. In the the Qenya Lexicon of the 1910s, Tolkien had two distinct roots for “similarity”: unglossed ᴱ√SĒ with variant ᴱ√SENE⁽²⁾ and derivatives like ᴱQ. se “as, like, in manner of” and ᴱQ. (a)sesta- “to liken, compare” (QL/82), and also ᴱ√VĪ “as” with variant ᴱ√VI‘I and derivatives like ᴱQ. ve “as, like”, ᴱQ. vealta- “to resemble”, and ᴱQ. vīkana- “compare” (QL/101). The semantic distinction between the two roots isn’t clear, and in the contemporaneous Gnomish Lexicon there was a third set of forms beginning with fel- such as G. fel “as, like”, G. feleg “equal”, and G. feltha- “resemble, seem like” (GL/34).
In later notes Tolkien proposed a variety of primitive origins for Q. ve “as, like”: ✶wē (we’e) in 1957 Quenya Notes (VT49/10; PE17/189), ✶bē from notes from the late 1950s or early 1960s (VT49/32 note #10), and ✶vai as a relative of suffixal -va in notes from 1968 (VT49/32 note #10). As there are not any definite Sindarin cognates for Q. ve in Tolkien’s published writings, it is hard to know which of these is more likely.
Neo-Eldarin: For purposes of Neo-Eldarin, I would go with primitive ✶bē as the most widely excepted option, producing S. ✱be “as, like”.
A primitive “dual” element mentioned in notes on numbers from the late 1960s, contributing to the forms of primitive ✶enekwe “six” and ✶yun(e)kwe “twelve” in the Quenya branch of Elvish, as well as the ancient 1st person inclusive pronoun ✶ñwe (VT48/10). It was probably related to the ancient dual suffix ✶-ū (Let/427). It was also likely a later iteration the dual root ᴱ√WI from the Qenya Lexicon of the 1910s which was likewise connected to dual U (QL/33). This early root was mentioned in the contemporaneous Gnomish Lexicon as ᴱ✶u̯i (GL/45).