A word derived from the Greek gnostikos, meaning one who has acquired gnosis or "knowledge" (literally, "one who knows"). Any of several Gnostic sects that flourished in the Mediterranean world during the time of Christ, particularly during the second and third centuries C.E. and for many centuries after. The two major branches of Gnosticism were Sethian or Jewish Gnosticism, and Valentinian or Christian Gnosticism.