early 15c., "monster of Greek mythology," from Latin Sphinx, from Greek Sphinx, literally" the strangler," a back-formation from sphingein "to squeeze, bind" (see sphincter).
Monster, having a lion's (winged) body and a woman's head, that waylaid travelers around Thebes and devoured those who could not answer its questions; Oedipus solved the riddle and the Sphinx killed herself. The proper plural would be sphinges. Transferred sense of "person or thing of mysterious nature" is from c.1600. In the Egyptian sense (usually male and wingless) it is attested from 1570s; specific reference to the colossal stone one near the pyramids as Giza is attested from 1610s.