sin (1) a word either meaning "thus" (adverb) or "this" (as an independent word in the sentence, not modifying another word like sina does). Attested in the sentence sin quentë Quendingoldo Elendilenna, either *"this Pengolodh said to Elendil" or "thus spoke Pengolodh to Elendil" (PM:401). Patrick Wynne argues that sin is an adverb "thus" derived from the stem si- "this (by me)" (VT49:18)
Quenya
sië
thus
sië
adverb. thus
silta
noun. sieve
cen
noun. sight, sight, *sense of sight
sin
thus
cénë
noun. sight
sië adv. "thus" (VT43:24, VT49:18)