Why is the ninth month called September?
mid-14c., crasen, craisen "to shatter," probably Germanic and perhaps ultimately from a Scandinavian source (e.g. Old Norse *krasa "shatter"), but entering English via an Old French form (cf. Modern French écraser). Original sense preserved in crazy quilt pattern and in reference to pottery glazing (1832). Mental sense perhaps comes via transferred sense of "be diseased or deformed" (mid-15c.), or it might be an image. Related: Crazed; crazing.
late 15c., "break down in health," from craze (v.) in its Middle English sense; this led to a noun sense of "mental breakdown," and by 1813 to the extension to "mania, fad," or, as The Century Dictionary (1902) defines it, "An unreasoning or capricious liking or affectation of liking, more or less sudden and temporary, and usually shared by a number of persons, especially in society, for something particular, uncommon, peculiar, or curious ...."