A word appearing as ᴱN. gwesg “weakly” in Early Noldorin Word-lists of the 1920s (PE13/146). This is the only Elvish word in the published corpus associated with weakness without extra connotations.

Neo-Sindarin: I would retain this word as ᴺS. gwesg and would further assume it can be used as both an adjective “*weak” as well as an adverb “weakly”. It is not clear what its etymology would be in Tolkien’s later conception of the languages, however (< √WESEK?)