late 14c., "a message from a god expressed by divine inspiration through a priest or priestess," in answer to a human inquiry, usually respecting some future event, from Old French oracle "temple, house of prayer; oracle" (12c.) and directly from Latin oraculum, oraclum "divine announcement, oracle; place where oracles are given," from orare "pray, plead" (see orator), with material instrumental suffix -culo-.
In antiquity, "the agency or medium of a god," also "the place where such divine utterances were given." This last sense is attested in English from early 15c. Extended sense of "uncommonly wise person" is from 1590s.