A noun for “light” derived from the root √KAL of similar meaning (PE17/50, 84), and appearing in the phrase Lacho calad! Drego morn! “Flame light! Flee night!” (UT/65). In one place it was glossed “light, fire, brightness, shining” (PE17/84), so it seems it could refer to any shining thing or source of light. For purposes of Neo-Sindarin, I would only use it in reference to “fire” as a source of illumination, not as a flame.
Conceptual Development: N. calad “light” appeared in The Etymologies of the 1930s, already with the derivation given above (Ety/KAL). In this document it was the basis for the final element of the name N. Gil-galad, and this was true in some later writings as well (PE17/50), but Tolkien eventually decided the second element of Gil-galad was (ñ)galad “radiance”, an element also seen in the name of Galadriel (PM/347).
_ n. _light, fire, brightness, shining. >> galad