Green’s Dictionary of Slang

1. an inquisitive person, a ‘nosey parker’.

1891		Century Mag. (N.Y.) 5733/2: snoop. [...] One who snoops, or pries or sneaks about; a snooper [DA].
1927		Press & Sun Bulletin (Binghamton, NY) 21 Jan. 6/2: America [...] is infested with spies, sneaks and busybodies [...] It is preyed upon by snoops who pry into the private affairs of other people.
1939		R.L. Bellem ‘Kill That Headline’ in Romantic Detective Feb. 🌐 He heard a man’s voice snarling: ‘Got the lousy snoop!’.
1946		J. Evans Halo in Blood (1988) 57: You – you snoop!
1959		E. De Roo Young Wolves 109: It was sensible to go into the office and check her schedule. But with those office snoops there might be too many questions asked.
c.1973		J. Thompson ‘Sunrise at Midnight’ in Fireworks (1988) 162: I don’t like snoops, so pull in your nose.
1974		(con. late 1940s) E. Thompson Tattoo (1977) 526: He was a snoop. A secret underwear sniffer.
1998		G. Burn Happy Like Murderers 199: He was an inquisitive person. He was a snoop. He was nosy.
2001		‘Randy Everhard’ Tattoo of a Naked Lady 148: There’s one thing you’re gonna learn about Butterfly – she don’t like snoops.

2. (US) an act of surveillance.

1920

A. Baer Two & Three 27 Feb. [synd. col.] Taking a flat-eyed snoop through the hole in papa’s weejee beard.

3. (orig. US) a (private) detective; also attrib.

1936		R.L. Bellem ‘Falling Star’ in Spicy Detective Sept. 🌐 Come on, snoop. Cough up that sparkler.
1947		S.J. Perelman ‘Farewell, My Lovely Appetizer’ in Keep It Crisp 13: I haven’t been a private snoop twelve years for nothing.
1957		‘Ed Lacy’ Lead With Your Left (1958) 89: There isn’t much work in the private snoop racket.
1978		J. Webb Fields of Fire (1980) 98: A CID is a snoop, man [...] Worked for Criminal Investigation Division.
1989		T. Blacker Fixx 155: Various snoops and noddies began to take an unhelpful interest.
1998		P. Doyle (con. late 1950s) Amaze Your Friends (2019) 159: ‘Did Irving tell you he’d hired other snoops?’.
2006		C. Hiaasen Nature Girl 209: Triumphs of solo surveillance, the greatest hits from his life as a snoop.

4. a suspicion, a cause of ‘snooping’.

1944

C.S. Montanye ‘Shoulder Straps’ in Thrilling Detective Feb. 🌐 ‘What’s the snoop, McClain?’ ‘What do you think?’ ‘I’ll guess. The Bronx job this morning.’.

5. a spy.

1970

A. Sillitoe Start in Life (1979) 343: His snoops already know I left Beirut.