Middle Primitive Elvish
kab
root. to be able, capable
kab
root. hollow
kab-
verb. can, I can
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 appearing as both √KAV and √KAB in verbal notes from the 1940s with glosses like “be able” and “capable” (PE22/105, 127). In this sense it was probably replaced by √POL in Tolkien’s later writing (PE17/181). It relationship to √KAB “hold, contain, retain” is unclear.