Green’s Dictionary of Slang

gumshoe n.

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

1. (also gumboot, gumshoer) a private detective or police officer.

[Nat. Police Gaz. 6 Dec. 125/1: Gum Elastic Police.— We understand that this title has been substituted for that of ‘Star Police’ [...] Whether it arises from the fact of their having adopted India rubber coats and shoes as their winter uniform [etc]].
[US]M. Kelly Little Citizens 127: The Associate Superindent for her vicinity was the Honourable Timothy O’Shea, known and dreaded as ‘Gum Shoe Tim,’ owing to his engaging way of creeping softly up back stairs and appearing all unheralded and unwelcome, upon the threshold of his intended victim.
[US]‘O. Henry’ ‘The Fifth Wheel’ in Strictly Business (1915) 66: You’re a funny kind of sleuth. You must be one of the Central Office gumshoers.
[US]H.A. Franck Zone Policeman 88 158: Everything on wheels was free to the ‘gumshoe’ except the ‘yellow car’.
[US]G.H. Mullin Adventures of a Scholar Tramp 26: He is known on the Road not only as ‘dick’ but [...] as ‘bull,’ ‘soft-shoe,’ ‘gum-shoe,’ an ‘elbow,’ a ‘flatty,’ or a ‘mug’.
[US]D. Hammett Red Harvest (1965) 21: So you’re a gum-shoe [...] What do you want to know now?
[US]R. Chandler ‘Blackmailers Don’t Shoot’ in Red Wind (1946) 77: Keep your paws off me, gumshoe!
[US]Mezzrow & Wolfe Really the Blues 131: We looked that gumshoe square in the eye.
[US]N. Algren Man with the Golden Arm 283: Evading fire dicks and gumboots, fingerprint experts and rookies in harness.
[US]R. Chandler Playback 87: Don’t call me ‘sister’, you cheap gumshoe!
[US]E. De Roo Big Rumble 137: ‘Guess we’ll never know, Mik,’ he sighed. ‘A wild goose chase. I’d make some gum-shoe.’.
[US]J.D. Horan Blue Messiah 197: The ‘gumshoers’—the Police Commissioner’s Confidential Squad, [...] was despised as deeply as the FBI.
[UK]N. Smith Gumshoe (1998) 15: ginley’s the name / gumshoe’s the game.
[US]J. Ellroy Brown’s Requiem 20: As far as the IRS knows, I’m a starving gumshoe.
[Aus]E. George ‘The Surprise of His Life’ Evidence Exposed (1999) 159: No one had ever complained about some two-bit gumshoe nosing into his background.
[UK]Guardian G2 22 Feb. 16: The gumshoes are already on the case.
[US]J. Ellroy Hilliker Curse 14: An equal number of gumshoes were stalking my mother.

2. (US, also gumshoer) a sneak thief or prowler.

[US]C.L. Cullen More Ex-Tank Tales 221: I thought you were a daylight gum-shoer for a minute.
[US]A.H. Lewis Confessions of a Detective 33: One of Red Bob’s gang had crept upon me, gumshoe fashion, and dealt me a blow.
[US]G. Henderson Keys to Crookdom 407: Gumshoe. One who sneaks.
[US]Monteleone Criminal Sl. (rev. edn).
[US]E. Hunter ‘See Him Die’ in Jungle Kids (1967) 106: Donleavy is playing the gumshoe, sneaking through the alley.

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

[US]Sun (NY) 18 Oct. 11/1: The big ring gumshoes ought to take a mooch around and find out who’s grabbed it all.

4. (US) a hanger-on.

[UK]C. MacInnes City of Spades (1964) 153: These ain’t no stage-door gumshoes, they’re my friends.

In compounds

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

1. a sneak thief, a street robber.

[US]C.L. Cullen Tales of the Ex-Tanks 352: I had got mine just outside his place by a couple of gumshoe artists.
J. Gregory Judith Of Blue Lake Ranch 299: [She’ll] make a great little gumshoe artist one of these days.

2. (US) a plain-clothes detective.

[US]J. Wilstach Under Cover Man 61: Aw, he looks like a gumshoe artist to me.
N. Moseley Teacher’s Manual for Military [...] Training 112: It is not necessary to be a gumshoe artist. It is prudent to cultivate the habit of watching the class as a whole.
[Aus]Hackworth & Sherman About Face 172: Some gumshoe artist was fiddling around and suddenly our numbers were on the vehicle.
gumshoe worker (n.) [worker n.1 ] (US Und.)

1. a private detective.

[US]J.M. Sullivan Criminal Sl. 11: Gumshoe worker—A private detective; a spotter.

2. a sneak thief.

[US](con. c.1900) AS X:1 (Feb.) gum, gumshoe or gumshoe worker. 1. A burglar or sneak thief. 2 a stool pigeon.
[US]Goldin et al. DAUL 88/1: Gumshoe-worker, n. (Obsolete) A sneak thief.

3. an informer.

see sense 2.