Merriam-Webster's Collegiate® Dictionary, 11th Edition
PARTNER
I. noun see: parcener
Date: 14th century
one that shares ; partaker,
2. one associated with another especially in an action ; associate , colleague , either of two persons who dance together, one of two or more persons who play together in a game against an opposing side, a person with whom one shares an intimate relationship ; one member of a couple, a member of a partnership especially in a business, one of the heavy timbers that strengthen a ship's deck to support a mast, partnerless adjective
II. verb
Date: 1611
transitive verb to join or associate with another as partner, to provide with a partner, intransitive verb to join as a partner