Green’s Dictionary of Slang

gumshoe n.

[lit. or fig. rubber-soled shoes used for creeping around, whether as investigator or thief]

1. [20C+] (also gumboot, gumshoer) a private detective or police officer.

2. [1900s–40s] (US, also gumshoer) a sneak thief or prowler.

3. in general use of sense 1, an authority.

4. [1950s] (US) a hanger-on.

In compounds

gumshoe artist (n.) [artist n. (1)]

1. [late 19C–1900s] a sneak thief, a street robber.

2. [1930s+] (US) a plain-clothes detective.

gumshoe worker (n.) [worker n.1 ] [1900s–50s] (US Und.)

1. a private detective.

2. a sneak thief.

3. an informer.