A word in the Gnomish Lexicon of the 1910s appearing as G. lumbri “foul weather”, an abstract elaboration of G. lum “[dark] cloud” (GL/55), based on the early root ᴱ√LUVU or ᴱ√LUB (LT1A/Luvier; QL/57; PME/57).

Neo-Sindarin: If adapting this word to Neo-Sindarin, I would revise it ᴺS. lummor, based on (hypothetical) primitive *lu(m)brĭ > lummṛ(e) > lummor, where *lu(m)brĭ is a strengthened variant of (hypothetical) primitive *lubrĭ that is my proposed basis for ᴺQ. lúrë “bad weather”. I think these derivations could remain valid since the root √LUB “shadow, darkness” survives in Tolkien’s later writings (PE17/168).