To smell very bad, or to seem suspicious or wrong about something.
From Old English 'recan' meaning to smoke or emit vapor; originally described actual smoke rising, then evolved to describe foul smells rising from something, then figuratively to describe suspicious behavior.
The word 'reeks' shows a beautiful metaphorical journey—it started meaning 'smoke rises' but now when someone says a situation 'reeks of corruption,' they're using the old smoking smell as a metaphor for something invisible and bad.
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