Green’s Dictionary of Slang

snitching n.

[snitch v.]

informing; also as adj.

[Aus]Vaux Vocab. of the Flash Lang. in McLachlan (1964) 266: snitch to impeach, or betray your accomplices, is termed snitching upon them. […] an informer, or tale-bearer, in general is called a snitch, or a snitching rascal, in which sense snitching is synonymous with nosing, or coming it.
[UK]Sl. Dict. 299: snitching is synonymous in thieves’ slang with ‘nosing’ and ‘peaching’.
[Aus]Crowe Aus. Sl. Dict. 77: Snitching, Nosing, and Peaching are synonymous terms, which mean turning traitor, giving information to the police, etc.
Courier-Jrnl (Louisville, KY) 7 May 3/5: ‘Snitching’ is the capital offense in the prison. For it ostracism and every form of social degredation possible [is] to be practiced by the ‘snitcher’s’ fellow prisoners.
[US]O.F. Lewis Amer. Prisons and Prison Customs 303: Thus did one of the earliest reform schools go on record as intolerant of ‘snitching,’ and of government through stool pigeons.
[US]J.T. Farrell World I Never Made 207: What a little stinker his snitching brother was [...] he’d pound every ounce of snitching out of the dumb little punk.
[US]W.R. Burnett High Sierra in Four Novels (1984) 288: They thought he was getting favours for snitching.
[US] ‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.
[US]C. Cooper Jr Scene (1996) 14: Snitchin bastard.
[US]B. Jackson Get Your Ass in the Water (1974) 156: They got the righteous dads and the so-called bads / and plenty of the snitching kind.
[US]T. Harris Silence of the Lambs (1991) 125: Snitching wouldn’t give him enough of a chance to show off.
[US](con. 1975) K. Scott Monster (1994) 10: If anybody get caught for this, ride the beef, ’cause ain’t no snitchin’ here.
[US]Simon & Burns Corner (1998) 65: As for snitching, that part of the code is also dead and buried.
[US]UGK ‘Life Is 2009’ 🎵 You need to take my advice and stop snitchin fool / Or you can close yo’ ears, and run yo’ mouth.

In compounds

snitching moon (n.)

a full moon, which ‘snitches’ criminals.

[US]D. Clemmer Prison Community (1940) 335/2: snitching moon, n. A full moon, making detection of burglars easier.