Why is the ninth month called September?
medieval European coin, late 14c., probably from Middle Dutch groot, elliptical use of adj. meaning "great, big" (in sense of "thick"); see great. Recognized from 13c. in various nations, in 14c. it was roughly one-eighth an ounce of silver; the English groat coined 1351-2 was worth four pence. Also cf. groschen.