The phrase "companion in crime" typically refers to a person who is a partner in illicit or illegal activities. There are various synonyms that can be used to describe this type of person, such as confederate, accomplice, collaborator, co-conspirator, partner in crime, or even a henchman. These words imply a level of trust and cooperation in breaking the law or engaging in morally questionable behavior. However, it is important to note that these terms carry negative connotations and are not suitable to use in a positive or neutral context. When describing a person's relationship with another person involved in crime, it is important to be mindful of the words used, as they can strongly influence the perception of the situation.