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)
Primitive elvish
thus
root. evil mist, fog, darkness; blow, cause an air movement, blow, cause an air movement; [ᴹ√] *smell, stench; [√] evil mist, fog, darkness
ñorthus, ñorsus (-þus), (stem ñorsúr-) noun Quenya equivalent of Sindarin Gorthu "Mist of Fear", a name of Sauron (PE17:183). The word is not capitalized as a name in the source.