expression, i-adjective
useless; in vain; not worth the effort
Expresses that an action yields no worthwhile result or that effort is wasted. Often used after a verb in the た form or with ～ても.
こんなに練習したのに、試合に負けてしまっては甲斐がない。
After all this practice, it would be pointless if we lost the match.
高いお金を払った甲斐がなかった。
It wasn't worth the high price I paid.
無駄 is a noun/adjective meaning 'waste' or 'futility', focusing on the lack of utility. 甲斐がない is a phrase emphasizing that effort did not bring a worthwhile result.
意味がない means 'meaningless' or 'there is no point', often more logical. 甲斐がない carries a stronger emotional nuance of unrewarded effort.
From 甲斐 (worth, effect) + がない (there is no). 甲斐 originally meant 'effect' or 'result', and the phrase developed to express that effort was not rewarded.