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”.
A noun for a “dead [person]” appearing its plural form in the phrase Dor Gyrth i Chuinar “Land of the Dead that Live” (Let/417) and its mutated class-plural form in the phrase Fui ’Ngorthrim “Paths of the Dead” (RC/526). It is clearly based on the root √ÑGUR “death”.