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.
_ n. _death. guru << gûru.