i-adjective
inexcusable; unjustifiable; unpardonable
Describes an act or situation that cannot be excused or justified; often used in negative form すまないこと or すまないと思う.
彼のしたことはすまないことだ。
What he did is inexcusable.
i-adjective
Expresses personal regret or a feeling of being sorry; often used as a casual apology, similar to すみません but more informal and masculine.
遅れてすまない。
Sorry I'm late.
迷惑をかけてすまないと思っている。
I feel sorry for causing you trouble.
interjection
Used as a casual interjection for apologizing or expressing gratitude; similar to すみません but more informal and typically used among close friends or by men.
See also: すみません
すまない、ちょっと通してくれ。
Excuse me, let me through.
すまない、助かったよ。
Thanks, you really helped me out.