Wiktionary
n. 1 (context UK slang English) A dishonest or disreputable person; a crook or rogue. 2 (context cricket English) A googly. 3 (context horse-racing English) A horse deliberately held back in order to lose a race.
WordNet
n. a cricket ball bowled as if to break one way that actually breaks in the opposite way [syn: googly, bosie, bosie ball]
Usage examples of "wrong 'un".
She must have seen I was a wrong 'un from the minute she laid eyes on me, and especially when she realised I was only romping her for the sake of a few nights' lodging.
I don't always know a wrong 'un when I meet one, but I do know when someone's straight.
But I know a wrong 'un when I sees her, sir, and your Miss Merridew weren't that road .
She was woman enough to be taken by his good looks and easy charm, but she sensed, I think, that here was a real wrong 'un, and confessed to me on one occasion that she was sure he was not a gentleman.