Early Quenya
nellume
adverb. *three times
neldellume
adverb. *three times
nel
adverb. thrice
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 word appearing in the Early Qenya Grammar of the 1920s as ᴱQ. nellume or neldellume clearly meaning “✱three times”, a combination of ᴱQ. nelde “three” and ᴱQ. -llume “times” (PE14/51, 84).
Neo-Quenya: I would retain ᴺQ. nellumë “thrice, three times” for purposes of Neo-Quenya since both elements remain in use in Tolkien’s later writings.