The Collaborative International Dictionary of English v.0.48:

Permutation \Per`mu*ta"tion\ (p[~e]r`m[-u]"t[=a]"sn[u^]n), n.
   [L. permutatio: cf. F. permutation. See Permute.]
   1. The act of permuting; exchange of the thing for another;
      mutual transference; interchange.
      [1913 Webster]

            The violent convulsions and permutations that have
            been made in property.                --Burke.
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   2. (Math.)
      (a) The arrangement of any determinate number of things,
          as units, objects, letters, etc., in all possible
          orders, one after the other; -- called also
          alternation. Cf. Combination, n., 4.
      (b) Any one of such possible arrangements.
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   3. (Law) Barter; exchange.
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   Permutation lock, a lock in which the parts can be
      transposed or shifted, so as to require different
      arrangements of the tumblers on different occasions of
      unlocking.
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The Collaborative International Dictionary of English v.0.48:

Alternation \Al`ter*na"tion\, n. [L. alternatio: cf. F.
   alternation.]
   1. The reciprocal succession of things in time or place; the
      act of following and being followed by turns; alternate
      succession, performance, or occurrence; as, the
      alternation of day and night, cold and heat, summer and
      winter, hope and fear.
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   2. (Math.) Permutation.
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   3. The response of the congregation speaking alternately with
      the minister. --Mason.
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   Alternation of generation. See under Generation.
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WordNet (r) 3.0 (2006):

alternation
    n 1: successive change from one thing or state to another and
         back again; "a trill is a rapid alternation between the two
         notes"