Green’s Dictionary of Slang

1. (UK society) the poor classes.

1909

J. Ware Passing Eng. of the Victorian Era.

2. (UK society) a postcard.

1889		E. Dowson letter 21 Feb. Letters (1967) 39: I enclose a P.C. wh. I had just written – it is no longer necessary – but you may as well post it .
1916		B.E.F. Times 1 Dec. (2006) 135: Drop a P.C. and our Mr. Jarrie will call on you.
1923		C.B. Poultney Mrs. ’Arris 39: Goo’-bye. Send us a P.C. [...] when you get there.
1953		K. Amis letter Dec. in Leader (2000) 354: If it isn’t too much bother, shoot me a pc with your reactions by return.
1966		P. White Solid Mandala (1976) 132: Dulcie’s p.-c. She sent me a card from some lake.

3. a police constable.

1900		‘Doss Chiderdoss’ ‘In-and-out Running’ Sporting Times 17 Feb. 1/4: ’Twas her own silverware, and a brace of p.c.’s / Were called in to upset the smart couple’s neat wheeze.
1947		N. Marsh Final Curtain (1958) 204: Running a murderer to earth is just a job to us, as copping a pickpocket is to the ordinary P.C.
1989		J. Morton Lowspeak 111: PC Hard – the officer who will interrogate a suspect roughly [...] to obtain a confession. If this treatment is not successful his colleague PC Soft will take over, sympathising with the man and offering him cigarettes.

4. (US) the Police Commissioner.

1953		F. Paley Rumble on the Docks (1955) 295: The P.C. was putting pressure on them.
1956		‘Toney Betts’ Across the Board 318: The P.C., the Police Commissioner’s squad.
1974		G. Radano Stories Cops Only Tell Each Other 115: ’Frank, you’re not from the police commissioner’s office, are you?’ [...] ‘Relax,’ he said. ‘No, I’m not from the P.C.’s office’ .
1994		M. McAlary Good Cop Bad Cop 56: The commissioner’s order went down the ladder: The PC doesn’t want to hear about corruption cases.

5. (US drugs/gambling) a percentage.

1956		‘Toney Betts’ Across the Board 318: P.C. Percentage.
1968		T. Thackrey Gambling Secrets of Nick The Greek 96: It only means that the house p-c on that particular part of the action is zero.
1989		(con. 1982–6) T. Williams Cocaine Kids (1990) 9: The runner earns a ‘p.c.,’ a part commission or percentage of the sale from the dealer.
1992		T. Williams Crackhouse 63: It could be to get customers to take them to the ‘spot’ so you could get yourself a ‘p-c,’ a percentage of the drug sale.

6. (drugs) a piece of crack cocaine.

1992

T. Williams Crackhouse 69: ‘P-c’ is sometimes translated as ‘piece of crack’ as well as ‘percentage’. These percentages are not fixed, but given at the dealer’s discretion.

7. (US prison) protective custody.

1992		S.L. Hills Tragic Magic 144: The PC block is where you have not only your rats but also the weak inmates – soft guys [...] and some of your animals are kept in protective custody – guys who can’t be put in the regular prison population.
2002		J. Lerner You Got Nothing Coming 62: P.C. in this joint is as bad as the Fish Tank or the fucking Hole — those dawgs sit in their houses twenty-four-seven.
2012		‘Dutch’ ? (Pronounced Que) [ebook] ‘You may want to ask to go to protective custody.’ [...] ‘P.C.?! Es tu loco?! I can’t fgo to P.C.’.
2016		Mother Jones July/Aug. 🌐 ‘I don't want to go on no PC, man,’ he says to me. He thinks they are going to put him in protective custody.