rock, adj. — Green’s Dictionary of Slang

rock adj.

1. excellent, outstanding. [i.e. it knocks one off-balance].

1944		D. Burley Orig. Hbk of Harlem Jive 146: Rock — Supreme pleasure, tops in dancing and music, finest esthetic delight.
1989		Eble Campus Sl. Mar. 7: rock – cool, awesome, or totally superior.
1997–2000		Da Bomb 🌐 24: Rock: 1. Elite; cool; fun; exciting; loud.
2009		T. Black Gutted 84: I’m rock. After the people-smuggling bust I’m...well, I’m solid.

2. very firm, adamant, uncompromising [SE rock-hard].

2001

K. Sampson Outlaws (ms.) 40: Membership’s rock though, Ray says. They’re strict as fuck who they’ll let in.

In compounds

Rock College (n.)

(N.Z. prison) one of a number of NZ prison establishments.

1942		M. Harcourt A Parson in Prison 164: [S]ome of the alumni of ‘Rock College’ - as the inmates call His Majesty’s Prison, Mount Eden - had battered the back door [...] in an attempt to burgle the house.
1988		McGill Dict. of Kiwi Slang 93: rock college prison.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 154/2: rock college 1 prison. Most frequently applied to Mount Eden Men’s Prison, Auckland, but also used less commonly to refer to a variety of other prisons, including Waikeria Prison, Kaitoke Prison, Invercargill Prison, Mount Crawford Prison and the old Napier Hill Prison 2 a borstal.

rock lobster (n.)

(N.Z. prison) a member of the Mongrel Mob biker/prison gang.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 155/1: rock lobster n. a member of the Mongrel Mob.

rock monkey (n.) [rock ape]

(N.Z. prison) a person of colourt, esp. a Pacific Islander.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 155/1: rock monkey (also rock ape) n. a person with dark skin, esp. applied to a Pacific Islander.