expression, i-adjective
unreliable; undependable; untrustworthy
Describes a person, thing, or information that cannot be relied upon. Often used in negative contexts to express doubt or warn against trusting something.
彼の言うことは当てにならない。
What he says is unreliable.
この天気予報は当てにならない。
This weather forecast is not to be trusted.
From 当て (expectation, reliance) + に + ならない (negative form of なる, to become). Literally 'does not become a reliance'.