noun

1. 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
2. either of two persons not married to each other but otherwise in an intimate, spouse-like relationship
3. Naut. a framework, as of timbers, for supporting a mast, capstan, etc. where it passes through the deck

Etymology: ME partener, altered (by assoc. with part, part) < parcener: see parcener

transitive verb

1. to join (others) together as partners
2. to be or provide a partner for