1620s, "of Delos," tiny island in the Aegean, birthplace of Apollo and Artemis. Delian problem "find the length of the side of a cube having double the volume of a given cube," was set by the oracle at Delos when it answered (430 B.C.E.) that the plague in Athens would end when Apollo's (cube-shaped) altar was doubled. The Latin fem. form of the word became the proper name Delia.
