Sindarin 

gwanwen

adjective. departed, departed, *gone, lost [to time], past

A word for “departed” in the Quendi and Eldar (Q&E) essay from 1959-60 (WJ/378), clearly derived from the root √ “away”. It might be related to the verb gwae- from Definitive Linguistic Notes (DLN) of 1959 (PE17/148). That verb had an irregular passive participle gwawn or gwanu. The word gwanwen may be a modification of (archaic?) gwanu from DLN to more strongly resemble other passive participles like govannen (LotR/209) or onnen (WJ/387). Alternately, it could be a simple adjective, the Sindarin equivalent of Q. vanwa.

Neo-Sindarin: I would assume that, like its Quenya equivalent, gwanwen has the added connotation of “✱gone, lost [to time], past” for purposes of Neo-Sindarin.

Conceptual Development: The Gnomish Lexicon of the 1910s had G. haim or haithin “gone, departed, lost”, the latter based on the verb G. haitha- “hie, go, fare, walk” (GL/47).