Green’s Dictionary of Slang

bull n.5

[Ger. sl. Bulle, police officer or poss. synon. Sp. sl. bul; orig. US but Aus./UK black use late 20C]

1. [late 19C+] (orig. US, also bul, a police officer; thus US tramp) bull buster, one who is obsessed with assaulting the police; fresh bull, a police officer who cannot be bribed; wise bull, a detective.

2. [20C+] a railroad security guard.

3. [20C+] (US prison) a prison warder; thus night bull, the night guard.

4. [1910s+] (US) a detective.

5. [1910s+] in comb., a certain kind of police officer, e.g. country bull, a local, small-town officer; narcotic bull, a Federal narcotic officer; motorcycle bull, motorcycle police officer; road bull, highway patrol officer.

In compounds

bull horrors (n.)

see separate entries.

bull simple (adj.)

[1930s–60s] (US tramp) frightened of the police.

bull taxi (n.)

[1910s] (US tramp) a police van used to transport prisoners, a Black Maria n. (1)

bull trap (n.) (also bully trap)

1. [19C] (US Und.) one who impersonates an official in order to extort money.

2. [1930s+] (Aus.) a villain who impersonates a police officer and preys on couples in lover’s lanes, extorting money from those who should not, for whatever reason, be there.

bullwagon (n.)

[1970s] (Aus.) a vehicle carrying suspects or criminals to a police station or prison.