O
- O-Po-Po
- Ontario, the Ontario Provincial Police.
- Old Bill
- A term in use in London among other areas, inspiring the television series The Bill. The origin of this nickname is obscure; according to the Metropolitan Police themselves, there are at least 13 different explanations.
- One Time
- A term, mostly used on the U.S. West Coast, that has been given numerous explanations, including: the idea that if one is arrested, it only takes "one time" to be put away (convicted); and that looking at police officers "one time" is enough to garner their attention and invite harassment.
- Other People
- Used in J.J. Connolly's Layer Cake to refer to the police.
Read more about this topic: List Of Police-related Slang Terms