noun

• (especially of a non-human animal) A breeding partner.
  "Such overt displays of avowed sexual prowess – or at least, desperate availability – are not limited to the countryside. Even in the city, birds and animals and stockbrokers and nurses find ways of signalling their suitability as a mate."
• (colloquial, British, Australia, New Zealand, Ireland, South Africa, sometimes elsewhere in the Commonwealth) A friend, usually of the same sex.
  "I'm going to the pub with a few mates."
• (colloquial, British, Australia, New Zealand, Ireland, South Africa, sometimes elsewhere in the Commonwealth) Friendly term of address to a stranger, usually male, of similar age.
  "Excuse me, mate, have you got the time?"
• (nautical) In naval ranks, a non-commissioned officer or his subordinate (e.g. Boatswain's Mate, Gunner's Mate, Sailmaker's Mate, etc).

verb

• (intransitive) To match, fit together without space between.
  "The pieces of the puzzle mate perfectly."
• (intransitive) To copulate.
  "“In fact, the apes live with us, and have for many ages. We call them the first men—we speak their language quite as much as we do our own; only in the rituals of the temple do we make any attempt to retain our mother tongue. In time it will be forgotten, and we will speak only the language of the apes; in time we will no longer banish those of our people who mate with apes, and so in time we shall descend to the very beasts from which ages ago our progenitors may have sprung.”"
• (intransitive) To pair in order to raise offspring.
• (transitive) To arrange in matched pairs.

noun

• (chess) Clipping of checkmate.

verb

• (chess) Clipping of checkmate.