Gnomish
lumbri
noun. foul weather
lumbrin
adjective. overcast
lumba
adjective. overcast
Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!
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).