noun, noun which may take the genitive case particle 'no'
incompetent person; worthless person; dimwit
A blunt, derogatory term for someone with no ability or talent. Often used as an insult or in self-deprecation. Can also function adjectivally with の.
彼は能無しだと陰で言われている。
He is called a worthless person behind his back.
こんな簡単なこともできないなんて、自分が
I feel like a total incompetent when I can't even do something this simple.
無能 is a more formal, objective term for incompetence or inability, often used in professional contexts. 能無し is a colloquial, insulting label for a person.
役立たず emphasizes uselessness or being of no help, while 能無し focuses on a lack of innate talent or ability.
Compound of 能 (ability, talent) + 無し (without). The reading のう is the on'yomi of 能, and なし is the classical terminal form of 無い.