What is the X in X-mas?
1610s, " to enter or be put in rivalry with," from Middle French compéter "be in rivalry with" (14c.), or directly from Late Latin competere "strive in common," in classical Latin "to come together, agree, to be qualified," later, "strive together," from com- "together" (see com-) + petere "to strive, seek, fall upon, rush at, attack" (see petition (n.)).
Rare 17c., revived from late 18c. in sense "to strive (alongside another) for the attainment of something" and regarded early 19c. in Britain as a Scottish or American word. Market sense is from 1840s (perhaps a back-formation from competition); athletics sense attested by 1857. Related: Competed; competing.