Unknown. Possibly alteration of Old Japanese浮かむ (ukamu, “to float”), modern 浮かぶ (ukabu). Alternatively, may derive from Middle Chinese雁 (/ngænH/, “a type of wild goose”), borrowed with the kan'on reading gan, with initial g changing to k due to the avoidance of voiced stops at the start of Japanese words, and final n changing to mu due to apparent lack of final n in Old Japanese.
(slang)(from the way ducks return to the same place and are thus easy to hunt) a mark or easy target for a swindle, someone who is likely to lose at gambling or other competition
(slang)(from the good flavor of duck meat) short for 鴨の味 (kamo no aji, “duck flavor”): a very good flavor; by extension, any remarkably good sensation or feeling, particularly describing happy marriedlife