Green’s Dictionary of Slang

half a sheet n.

[based on half a note n.]

(UK prison) a punishment for wardens, usu. a fine.

Show quotations
[UK]F. Norman in ‘Encounter’ n.d. in Norman’s London (1969) 63: Darbies (handcuffs), PO (Principal Officer), piss hole (lavatory), meat wagon (black maria), half a sheet (punishment that screws get, usually a fine).