If someone say 'She smells fishy'
What does the phrase mean exactly?
'she smells of fish' or 'she's hiding something'?
If it's the former, How do we express the latter with the same word?
thanks in advance.
As Ron said, if someone is fishy they smell of fish. If she's obviously hiding something, her behaviour is fishy. A suspicious thing or situation is "fishy" in the metaphorical sense.