Quenya 

Silmaril

radiance of pure light

Silmaril (Silmarill-, as in pl. Silmarilli), noun, name of the shining jewels made by Fëanor; full sg. form Silmarillë (SA:sil, SIL, RIL, MIR).Translated "radiance of pure light" in Letters:148. Gen. pl. Silmarillion, as in (Quenta) Silmarillion "(the Story) of the Silmarils".