S. lach n. “(leaping) flame” (Category: Flame)
An element meaning “flame” appearing in many names. Christopher Tolkien gave its form as lhach “leaping flame” in the Silmarillion appendix (SA/lhach), but given Lachend “Flame-eyed” (WJ/384) and lacho calad! “flame light!” (UT/65), I think *lach is the likelier Sindarin form, which is the form also suggested by Hiswelókë’s Sindarin Dictionary (HSD).
Conceptual Development: ᴱN. lhacha “flame” appeared in Early Noldorin Word-lists of the 1920s (PE13/148).
References ✧ SA/lhach; WJ/384