Source : Webster's Revised Unabridged Dictionary (1913)

Pairing \Pair"ing\, n. [See {Pair}, v. i.]
   1. The act or process of uniting or arranging in pairs or
      couples.

   2. See {To pair off}, under {Pair}, v. i.

   {Pairyng time}, the time when birds or other animals pair.

Pair \Pair\, v. i. [imp. & p. p. {Paired}; p. pr. & vb. n.
   {Pairing}.]
   1. To be joined in paris; to couple; to mate, as for
      breeding.

   2. To suit; to fit, as a counterpart.

            My heart was made to fit and pair with thine.
                                                  --Rowe.

   3. Same as {To pair off}. See phrase below.

   {To pair off}, to separate from a company in pairs or
      couples; specif. (Parliamentary Cant), to agree with one
      of the opposite party or opinion to abstain from voting on
      specified questions or issues. See {Pair}, n., 6.

Source : WordNet®

pairing
     n 1: the act of pairing a male and female for reproductive
          purposes; "the casual couplings of adolescents"; "the
          mating of some species occurs only in the spring" [syn:
          {coupling}, {mating}, {conjugation}, {union}, {sexual
          union}]
     2: the act of grouping things or people in pairs