A Sindarin word for “death” derived from primitive ✶ñgurū (PE17/87), unusual in that its primitive ancient vowel u did not vanish. In The Etymologies of the 1930s Tolkien had variant forms [N.] gûr and gurw “death” marked with a “?”, both derived from Old Noldorin nguru and indicating some uncertainty on the exact phonetic developments (EtyAC/ÑGUR). Elsewhere in The Etymologies Tolkien said that [N.] guru was “Death as state or abstract”, as opposed to [N.] gwanw or gwanath for the “act of dying” (Ety/GWAN).
Neo-Sindarin: For purposes of Neo-Sindarin, I would assume guru was for death as an abstraction or principle, and for the death of individuals I would use either gurth or gwanu/gwanath; see those entries for discussion.
The usual Sindarin word for “death”, derived from the root √ÑGUR of similar meaning (UT/39; Ety/ÑGUR).
Conceptual Development: This word dates all the way back to the Gnomish Lexicon of the 1910s (GL/43), anchored by well established names like Gurthang or Gurtholf(in), the name of Túrin’s sword. Tolkien experimented with various alternate forms over the years, such as G. urthu (GG/14), G. gurthu (GL/43), ᴱN. gurdh (PE13/146) and N. guruth (Ety/ÑGUR), but kept coming back to gurth as the basic form.
Neo-Sindarin: For purposes of Neo-Sindarin, I would use this word for death in general and especially violent death, as opposed to the more euphemistic [N.] gwanath or gwanu “death”, more literally “departure”.