Why is the ninth month called September?
late 13c., yrichon "hedgehog," from Old North French *irechon (cf. Picard irechon, Walloon ireson, Hainaut hirchon), from Old French herichun "hedgehog" (Modern French hérisson), formed with diminutive suffix -on + Vulgar Latin *hericionem, from Latin ericius "hedgehog," from PIE root *gher- "to bristle" (cf. Greek kheros "hedgehog;" see horror).
Still used for "hedgehog" in non-standard speech in Cumbria, Yorkshire, Shropshire. Applied throughout 16c. to people whose appearance or behavior suggested hedgehogs, from hunchbacks (1520s) to goblins (1580s) to bad girls (c.1530); meaning "poorly or raggedly clothed youngster" emerged 1550s, but was not in frequent use until after c.1780. Sea urchin is recorded from 1590s (a 19c. Newfoundland name for them was whore's eggs).