Green’s Dictionary of Slang

penitentiary adj.

SE in slang uses

In compounds

penitentiary agent (n.) [SAmE penitentiary agent; a prison officer who transports prisoners from a local jail to a penitentiary]

(US Und.) a lawyer who seems to be working more for the courts and police than for the defence of their client.

[US]D. Clemmer Prison Community (1940) 334/2: penitentiary agent, n. A shyster, or double crossing lawyer.
[US]Ragen & Finston World’s Toughest Prison 812: penitentiary agent – A public defender (A lawyer appointed by the Court).
penitentiary dispatcher (n.) [the professional inadequacies of court-appointed lawyers, whose clients often end up in the penitentiary]

(US Und.) a public defender.

[US]S. Morgan Homeboy 141: No wonder they call you guys Penitentiary Dispatchers.
penitentiary highball (n.) [highball n.1 (1)]

(US prison) home-brewed prison alcohol, based on strained shellac and milk.

[US]Goldin et al. DAUL 155/1: Penitentiary highball. (P) A mixture of strained shellac and milk. [Note: The shellac is run through cheesecloth or through the pithy part of a loaf of bread; the denatured alcohol is thus almost freed of gums and resins. Milk is added as an antidote.].
Reverend Glasseye & His Wooden Legs song title on Black River Falls [album] Penitentiary Highball.
penitentiary shot (n.) (also pen shot) [pen n.2 + shot n.1 (6b)]

(US drugs/prison) an injection achieved by using a rudimentary ‘needle’, in fact a pin and a medicine dropper; the pin is pushed into the vein and the dropper, filled with a solution of heroin and water, pushed over it.

[US]D. Maurer ‘Lang. of the Und. Narcotic Addict’ Pt 2 in Lang. Und. (1981).
[US]J.E. Schmidt Narcotics Lingo and Lore 142: Penitentiary shot [...] Pen shot – The injection of a narcotic [...] using improvised equipment.