Why is the ninth month called September?
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." Financial sense is from 1911. Related: Pyramidal.
pyramid pyr·a·mid (pĭr'ə-mĭd)
A solid figure with a polygonal base and triangular faces that meet at a common point.
A structure or part shaped like a pyramid.