Why is the ninth month called September?
late 13c., "close-fitting cap," from Old French coife "skull-cap, cap worn under a helmet, headgear" (12c., Modern French coiffe), from Late Latin coifa "a cap, hood" (source of Italian cuffia, Spanish cofia, escofia), of West Germanic origin (cf. Old High German kupphia, Middle High German kupfe "cap").
mid-15c., "to cover with a cap," from Middle French coiffer, from Old French coife (see coif (n.)); sense of "to arrange the hair" is attested in English from 1835. Related: Coifed; coifing.
close-fitting cap of white linen that covered the ears and was tied with strings under the chin, like a baby's bonnet. It appeared at the end of the 12th century as an additional head protection worn under the hood by men, and it persisted into the 16th century as ecclesiastic or legal headgear, sometimes worn alone, sometimes as an undercap.