甲斐

Meaning: “result”

From Old Japanese. First attested in the Man'yōshū of 759. Derived from the 連(れん)用(よう)形(けい) (ren'yōkei, “stem or continuative form”) of the verb 代(か)う (kau, “to exchange or replace one thing with another”), with the basic sense being "that which should be the result, outcome, or replacement".