requisite adj.

late 14c., requeren, "to ask (someone) a question, inquire," a sense now obsolete, from Old French requerre, requerir "seek, procure; beg, ask, petition; demand," from Vulgar Latin *requaerere, from Latin requirere "seek to know, ask, ask for (something needed)," from re-, here perhaps meaning "repeatedly" (see re-), + quaerere "ask, seek" (see query (v.)). In some later English senses probably directly from Latin.

Still in 16c.-17c. commonly "to ask or request (to have or do something)," but this original sense of the word has been taken over by request (v.).

Also from late 14c. as "to stand in need of, want; to need for some end or purpose." The sense of "demand that (someone) do (something)" is from 1751, via the notion of "to ask for imperatively, or as a right" (late 14c.). The meaning "demand as necessary or essential on general principles" is from early 15c. Related: Required; requiring.

1630s (n.) "a thing or condition required beforehand," 1650s (adj.), "required beforehand, necessary as a condition of something following;" see pre- "before" + requisite. A verb prerequire "require beforehand" is attested from 1610s.