company bull
n. a detective or guard who works for a private firm.Pete is a company bull for Acme Systems. He works nights.The company bull asked what we were doing there.
crapper dick
n. a police officer or detective who patrols public toilets.When he flubbed up the Wilson case, they made him a crapper dick in the central business district.What's a crapper dick get paid?
dick
n. a detective. (Underworld. From detective.)Some dicks were around looking for you.Barlowe is a private dick who has to keep one step ahead of the cops.
gumshoe
n. a policeman or a detective. (Underworld. Also a term of address. So-named for wearing silent, gum-rubber soles.)Has that gumshoe been around asking questions again?Look, gumshoe, what do you want with me?
private eye
n. a detective who is licensed to work privately rather than for a police department.I worked for a while as a private eye.The cops don't like private eyes much.