expression, i-adjective
Abbreviation of やむを得ない; used in casual or spoken Japanese to express that a situation is inevitable or there is no choice.
See also: やむを得ない
Since it started raining, canceling the picnic can't be helped, right?
急な出費だけど、必要ならやむない。
It's a sudden expense, but if it's necessary, it's unavoidable.