Synonyms for partner

These nouns all denote one who is united or associated with another, as in a venture or relationship. A partner participates in a relationship in which each member has equal status: a partner in a law firm.
A colleague is an associate in an occupation or a profession: a colleague and fellow professor.
An ally is one who associates with another, at least temporarily, in a common cause: countries that were allies in World War II.
A confederate is a member of a confederacy, a league, or an alliance or sometimes a collaborator in a suspicious venture: confederates in a scheme to oust the chairman.