Green’s Dictionary of Slang

ninja n.

[the 1980s TV cartoon Teenage Mutant Ninja Turtles, thus the colour green (like the cartoon heroes), of the pill and of the officers’ uniforms]

(S. Afr. prison) a prison warder.

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[SA]Mail & Guardian (Johannesburg) 3 Sept. 🌐 I heard Nelani scream, as the ninjas electroshocked him.

In compounds

ninja turtle (n.)

1. (N.Z. prison) a 200 mg tablet of morphine sulphate.

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[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 124/2: ninja turtle n. 1 a 200mg morphine sulphate tablet.

2. (N.Z. prison) a prison officer or member of the riot squad.

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[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 124/2: ninja turtle n. 2 (also ninja) a member of the Riot Squad 3 a prison officer.