ᴹ√DUB root. “lie, lie heavy, loom, hang over oppressively (of clouds)”
A root in The Etymologies of the 1930s glossed “lie, lie heavy, loom, hang over oppressively (of clouds)” with derivatives like ᴹQ. lumna “burdensome, oppressive, ominous” and N. dofn “gloomy” (Ety/DUB). In later writings, the similar Quenya word Q. lumba “gloomy” was derived from the root √LUM/LUB “shadow, darkness”, but the root ᴹ√LUM “*shadow” coexisted with ᴹ√DUB in The Etymologies, so perhaps it also survived later as an independent root (or was the result of d/l variation with √LUB).
References ✧ Ety/DUB; EtyAC/LUB