Describes a person, effort, or situation as lacking value or being beyond hope. Often used in set phrases like 甲斐なしの人生 or 甲斐なしな奴.
He led a worthless life.
Throw away such hopeless thoughts.
役立たず is a more direct 'useless person/thing', often colloquial, whereas 甲斐なし has a literary, somewhat old-fashioned tone.
Standard kanji-kana mixed spelling.
Alternate spelling using the kanji 無 for なし.
Compound of 甲斐 (かい, 'worth, effect') and なし ('without'). The exact historical derivation is uncertain, but the word has been used since classical Japanese to express futility or lack of value.