Longman Dictionary of Contemporary English
Wiktionary
vb. 1 (context auxiliary English) (non-gloss definition: Indicating duty or obligation.) 2 (context auxiliary English) (non-gloss definition: Indicating advisability or prudence.) 3 (context auxiliary English) (non-gloss definition: Indicating desirability.) 4 (context auxiliary English) (non-gloss definition: Indicating likelihood or probability.)
Usage examples of "ought to".
But I tell you as an engineer what you ought to know better than I do, that sort of work is no more related to unbinding locks and stealing vehicles than a minestrone is to a manticore.
It occurred to me that maybe I ought to find a place where I could hide in case someone came upstairs.
Sometimes he wondered if he ought to believe so peculiar a story, but he did find the details titillating.
I looked back at Shiara and opened my mouth to ask why we ought to leave, but I stopped before I said anything.
He ought to be ready to die here if what he'd been saying was true.