Wiktionary
oughtn't
contraction 1 (context UK English) ought not. 2 (context US Canada dated rare English) ought not.
Usage examples of "oughtn't".
She can't die, and she mustn't be in want, and she oughtn't to be a burden.
It's your father's idea that I ought to go into business and that you oughtn't to be engaged to me until I do.
So, as we couldn't play together like good children, of course it was plain that we oughtn't to play at all.
It isn't very pleasant to be thrusting yourself on a person you know doesn't want you--but I knew you oughtn't to be left all alone in the world.
But it oughtn't to be altogether my fault, because, you know, I don't see them nor have nothing to do with them except when they're on me.