Green’s Dictionary of Slang

monster n.

1. (US) a large and formidable car or plane.

[[UK]Sterne Tristram Shandy (1949) 130: Imagine to yourself, Obidiah mounted on a monster of a coach-horse].
[US]Ade Hand-made Fables 245: It was a beautiful Monster, with the sheen of Satin, the well-ordered compactness of a Swiss Watch, and a Purr like that of a Pet Kitten.

2. (US) an outstanding person, thing, achievement or success.

[US]C. Himes Real Cool Killers (1969) 19: (to a policeman) Hold it, monster.
[US]Baker et al. CUSS 158: Monster A strong, often offensive male.
[US]Newsweek 24 Mar. 81: The Average White Band is an exciting group with the potential to be what the music business calls ‘monsters’.
[UK]K. Sampson Powder 294: This can be the difference between a gold record and a mult-eye fuckin platinum monster!

3. (US campus) a difficult course or examination.

[US]Baker et al. CUSS.

4. in drug uses.

(a) (drugs) any exceptionally powerful drug.

[US]Milner & Milner Black Players 150: Mitchell extolled the virtues of shooting cocaine. ‘It’s a monster,’ he said.

(b) (US drugs) methedrine.

[US]L. Pettiway Workin’ It 14: Then it was monster. I never did use heroin. Yeah, I started mainlining monster at twenty-one.

5. an obsessive, an addict.

[US] Hip-Hop Connection Dec. 14: Self confessed beer and beats monster.
[UK]B. Hare Urban Grimshaw 202: Rave-loving, mad-driving, rap-talking party monsters.

6. (US prison) HIV/AIDS.

[US]Other Side of the Wall: Prisoner’s Dict. July [Internet] Monster: HIV. ‘He has the Monster.’.
Express Gay News No. 97 [Internet] Past Scenarios winners include 15-year-old Tex-Mex girls who explored teen pregnancy, and three inmates on Rikers Island who wrote The Monster (street slang for AIDS).

7. cocaine.

[US]ONDCP Street Terms 15: Monster — Cocaine.

SE in slang uses

In compounds

Monster Mansion (n.)

(UK Und.) a prison housing sex offenders and other extreme offenders.

[UK]N. ‘Razor’ Smith Raiders 275: Since 1999 [...] Albany [prison] has been known as Monster Mansion II, HMP Wakefield being the original Monster Mansion, because it now houses only sex offenders and other horrible specimens.

In phrases

make a monster of (v.)

to cuckold.

[UK]Shakespeare Hamlet III i: If thou wilt needs marry, marry a fool; for wise men know well enough what monsters you make of them.