Middle Primitive Elvish
(n)dub
root. lay base, foundation, root; found
dub
root. lie, lie heavy, loom, hang over oppressively (of clouds)
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
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).