Green’s Dictionary of Slang

1. describing a private detective or police officer, e.g. gumshoe man, gumshoe guy.

1899–1900		C.L. Cullen Tales of the Ex-Tanks 296: ‘You and this gum-shoe sleuth of yours are up in the air,’ I said to the desk sergeant.
1903		Tacoma Times (WA) 28 Dec. 3/5: The 18-Karat gumshoe stars of the New York detective force are frothing at the mouth.
1903		Nebraska State Jrnl (Lincoln, NE) 14 June 9/6: They’re in the hands of private flys — the unofficial gum-shoe people with the badges.
1903		Tacoma Times (WA) 28 Dec. 3/5: Mable Parker watched the gum-shoe men on the stand, heard them tell how they has trapped her, and laughed.
1906		A.H. Lewis Confessions of a Detective 198: Cull, you’re d’gum-shoe guy I was waitin’ fer, see!
1911		‘Sing Sing No. 57,700’ My View on Books in N.Y. Times Mag. 21 May 7/5: There’s a gum-shoe man in this that will make you feel like staving in his slats.
1913		H.A. Franck Zone Policeman 88 143: There was nothing for me to do but to descend to the ‘gumshoe’ desk in Ancon station.
1930		M. Fiaschetti You Gotta Be Rough 32: The Police Department nowadays has a detective school with lectures and blackboards and all that for educating gumshoe sleuths, but in my time the college course for dicks was simpler.
1935		A.J. Pollock Und. Speaks n.p.: Gum shoe man, a detective.
1945		R.L. Bellem ‘Coffin for a Coward’ in Hollywood Detective Dec. 🌐 I want to save up a retirement fund before some wise disciple puts a pistol period on my gumshoe career.

2. of an action, surreptitious, undercover; pertaining to being a private detective or police officer.

1899–1900		C.L. Cullen Tales of the Ex-Tanks 377: I did such a good gum-shoe stunt that he didn’t know there was anybody around.
1905		H. Green Actors’ Boarding House (1906) 279: He did a little gumshoe work, craftily stealing down the halls.
1907		B. Fisher A. Mutt in Blackbeard Compilation (1977) 8: I’m an old hand at this gum shoe stuff.
1911		S. Ford Torchy 159: Mr. Pepper don’t like the idea, though, of doin’ the gumshoe sneak.
1921		Morn. Tulsa Dly World (OK) 23 Jan. 1/4: [headline] ‘Gumshoe’ Investigations Against Governor Expunged.
1948		Dan Burley ‘Back Door Stuff’ 27 Nov. [synd. col.] His ‘quiet little wife’ has a list, courtesy of the gumshoe Dept., [...] of all the outside women he’s chasing.
1954		Johnson Black Widow [film script] What’s the reason for all this gumshoe work? [HDAS].
1991		(con. 1966) W. Kross Splash One 83: Not eye-wash, real gumshoe intell.
2006		C.W. Ford Deuce’s Wild 83: Look, I run a security and intelligence agency, not a gumshoe squad.
2011		J.J. DeCeglie Drawing Dead [ebook] An underground carpark. Basement floor. Real gumshoe spot.