partner

A partner is a person who takes part in an activity or business with others or one of two people who are in a relationship. (noun)

See partner in Webster's New World College Dictionary

noun

a person who takes part in some activity in common with another or others; associate; specif.,
1. one of two or more persons engaged in the same business enterprise and sharing its profits and risks: each is an agent for the other or others and is liable, except when limited to his or her own investment, for the debts of the firm
2. a husband or wife
3. either of two persons dancing together
4. either of two players on the same side or team playing or competing against two others, as in bridge or tennis
either of two persons not married to each other but otherwise in an intimate, spouse-like relationship
Naut. a framework, as of timbers, for supporting a mast, capstan, etc. where it passes through the deck

transitive verb

See partner in American Heritage Dictionary 4

(pärtˈnər)

noun

One that is united or associated with another or others in an activity or a sphere of common interest, especially:
a. A member of a business partnership.
b. A spouse.
c. A domestic partner. See Usage Note at domestic partner.
d. Either of two persons dancing together.
e. One of a pair or team in a sport or game, such as tennis or bridge.
Nautical A wooden framework used to strengthen a ship's deck at the point where a mast or other structure passes through it. Often used in the plural.