n. 1 a (in full imperial gallon) Brit. a measure of capacity equal to eight pints and equivalent to 4546 cc, used for liquids and corn etc. b US a measure of capacity equivalent to 3785 cc, used for liquids. 2 (usu. in pl.) colloq. a large amount. gallonage n.
[ ME f. ONF galon, OF jalon, f. base of med.L galleta, galletum, perh. of Celtic orig. ]