mate 1 
(māt)
(māt)n.
1. One of a matched pair: the mate to this glove.
2. A spouse or romantic partner.
3.
a. Either of a pair of birds or other animals that associate in order to propagate.
b. Either of a pair of animals brought together for breeding.
c. Either of a pair of plants, fungi, or other organisms that engage in sexual reproduction or conjugation with each other.
4.
a. A person with whom one is in close association; an associate.
b. Chiefly British A good friend or companion.
c. A person with whom one shares living quarters. Often used in combination: advertised for a new flatmate.
5. A deck officer on a merchant ship ranking next below the master.
6. A US Navy petty officer who is an assistant to a warrant officer.
v. mat·ed, mat·ing, mates
v.tr.
1. To join closely or combine: an engine that is mated to a four-speed transmission.
2. To cause to be united in marriage or a romantic sexual relationship.
3. To cause (organisms) to breed or bring (organisms) into close proximity for breeding.
v.intr.
1. To become joined in marriage or a romantic sexual relationship.
2.
a. To be paired for reproducing; breed.
b. To engage in sexual reproduction or conjugation.
[Middle English, from Middle Low German gemate, mate, messmate.]