" Smell something fishy "
Meaning:
Detect that something isn't as it should be.
Example:
He's always hanging around outside the women's dorm with a camera. It looks a bit fishy to me.
Where did it originate?:
Britain, 19th century. Deriving from an allusion to things that are 'as slippery as a fish'.
Where is it used?:
Mostly Britain.
Hear the idiom spoken:
