Early Primitive Elvish
kirisi
root. cut, split
kisi
root. cut, split
kiři
root. cut, split
kiði
root. cut, split
faka Speculative
root. cut
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 hypothetical early root to explain words in the Gnomish Lexicon of the 1910s such as G. fag- “cut” and G. fanc “cut” (GL/33). It might be related to ᴱ√FḶKḶ “cleave, hew”. There are no signs of this root in Tolkien’s later writing.