A detective or private investigator, especially one who works on cases discreetly.
American slang from the early 1900s, likely combining 'gum' (to sneak around) and 'shoe' (footwear), referring to the quiet rubber-soled shoes detectives wore to avoid detection.
This is pure American slang from the detective fiction boom! Gumshoes literally wore rubber-soled shoes for sneaking around, and the term stuck—it's one of those wonderful words that shows how jobs and their tools create slang.
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