Middle Primitive Elvish
say
root. know, understand
kwet
root. say
ab
root. refuse, deny, say no; away, go away, depart
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 in The Etymologies of the 1930s glossed “know, understand” with derivatives ᴹQ. saira “wise” and ᴹQ. sairon “wizard” (Ety/SAY). It is probably connected to later words like Q. alasaila “unwise” (PE22/154) and S. sael “wise” (MR/305) in documents from the 1950s and 60s, as suggested by Carl Hostetter (VT41/18).