1550s (earlier in Latin form piramis, late 14c.), from French pyramide (Old French piramide "obelisk, stela," 12c.), from Latin pyramides, plural of pyramis "one of the pyramids of Egypt," from Greek pyramis (plural pyramides) "a pyramid," apparently an alteration of Egyptian pimar "pyramid."
Greek pyramis also meant "kind of cake of roasted wheat-grains preserved in honey," and in this sense is said to derive from pyros "wheat" on the model of sesamis. According to some old sources the Egyptian pyramids were so called from their resemblance to the form of the cake, but Beekes points out that "the form of the cake is actually unknown."
Financial sense is from 1911. Related: Pyramidal.