Why is the ninth month called September?
early 13c., from Old French hanche (12c.) "hip, thigh; haunch," from a Germanic source, perhaps Frankish *hanka (cf. Old High German hinkan "to limp," ancha "leg," literally "joint;" Middle Dutch hanke "haunch"). "It is only since the 18th c. that the spelling haunch has displaced hanch" [OED]. Related: Haunches.