Qenya
lumbe
noun. gloom, shadow
ungwe
noun. gloom
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 noun in The Etymologies of the 1930s glossed “gloom, shadow” derived from the root ᴹ√LUM (Ety/LUM). It was an element in the name ᴹQ. Hísilumbe for N./S. Hithlum, more typically given as Q. Hísilómë. However, both the root √LUM “shadow” and derived Quenya words like Q. lumbulë “heavy shadow” continued to appear in Tolkien’s later writings (PE17/168; RGEO/59), so I suspect lumbe may remain valid as well.
Conceptual Development: A possible precursor is ᴱQ. lōmin “shade, shadow” from the Qenya Lexicon of the 1910s derived from the early root ᴱ√LOMO (QL/55).