Green’s Dictionary of Slang

1. (US Und.) a diamond thief.

1926		J.J. Finerty Criminalese.
1931		G. Milburn ‘Convicts’ Jargon’ in AS VI:6 439: ice man, n. A jewel thief.
1949		Monteleone Criminal Sl. (rev. edn).
1953		W. Brown Monkey On My Back (1954) 112: Pepe had confided to me that Rico was one of the ‘ice-men’.
1989		J. Morton Lowspeak.

2. an emotionless person.

1941		J. Lilienthal Horse Crazy 87: An iceman, in race-track slang, is a gambler who never loses his head [W&F].
1964		R. Buehler Annotated Collection of Obscene Humor 35: ‘Is the ice-man coming?’ ‘Not yet, but he’s breathing hard.’.
1977		E. Torres Q&A 131: Cold man [...] He is an ice man.
1998		K. Anderson Night Dogs 181: ‘Ice-man–they all saying, “Hanson some kind of cold motherfucker. Knocking ladies down”’.
1999		(con. 1979–80) A. Wheatle Brixton Rock (2004) 18: The youths who knew Brenton well thought of him as being an ice-man, but he had his fears.
1999		Observer Business 25 July 7: Pfeiffer was regarded by Wall Street as something of an ice man, keeping analysts and bankers at a distance.
2012		D. Spivey ‘If You Were Only White’ 62: Paige would [...] earn the reputation of being unflappable, cool as they come, the ice man.

3. a paid killer, a ‘hit man’.

1972		D. Pendleton Boston Blitz (1974) 12: ‘Whatta you want here with me?’ ‘Figure it out,’ the ice man suggested.
1989		J. Morton Lowspeak.
2000		(con. 1940s–60s) Décharné Straight from the Fridge Dad.
2012		G. Pelecanos (con. 1972) What It Was 182: He wasn’t one of those robot killers, what they called ice men.

4. one, e.g. a corrupt police officer, who is given bribes by gangsters etc.

1961		J. Scarne Complete Guide to Gambling.
1988		D. Woodrell Muscle for the Wing 184: After this I’m the iceman, eh? [...] For sure?

5. the frontman who pays or receives protection money on behalf of illegal gamblers or the authorities.

1961		J. Scarne Complete Guide to Gambling.
1989		J. Morton Lowspeak.