One who kidnaps cats, or alternatively, one who takes catnaps (identical spelling with different meaning).
From cat + napper (one who naps). The term can mean either sense, though the 'kidnapper of cats' meaning is rarer and more archaic.
This is a fantastic example of word homonymy—the same spelling means two completely different things! A catnapper could be someone caught on camera stealing your beloved pet, or your coworker dozing at their desk. Context is everything!
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