Early Quenya
sunqe
noun. going-down, descent, down-fall; abyss, depth
lanta-
verb. to fall
suq-
verb. to fall, fail, go down, die down
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 Qenya Lexicon of the 1910s meaning “going-down, descent, down-fall” as well as “abyss, depth”, derived from the early root ᴱ√SUQU (QL/87). In the Poetic and Mythological Words of Eldarissa it was only glossed “abyss” (PME/87).