alternation

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"
    

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.
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            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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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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97 Moby Thesaurus words for "alternation":
      Lissajous figure, back-and-forth, battledore and shuttlecock, beat,
      chain, coaction, coming and going, commutation,
      complementary distribution, concurrence, consecution, cooperation,
      counterchange, cross fire, cyclicalness, ebb and flow, engagement,
      exchange, fluctuation, flux and reflux, give-and-take, interaction,
      interchange, intercommunication, intercourse, interlacing,
      intermeshing, intermittence, intermittency, intermutation,
      interplay, intertwining, interweaving, interworking, lex talionis,
      measure for measure, mesh, meshing, meter, mutual admiration,
      mutual support, mutual transfer, mutuality, order, oscillation,
      pendulation, pendulum motion, periodicalness, periodicity,
      permutation, piston motion, progression, pulsation, quid pro quo,
      reappearance, reciprocality, reciprocation, reciprocity,
      recurrence, regular wave motion, reoccurrence, repetition,
      retaliation, return, reversion, rhythm, rhythmic play, rotation,
      row, seasonality, seesaw, seesawing, sequel, sequence, series,
      shifting, shuffling, sine wave, something for something,
      succession, teeter, teeter-totter, teeter-tottering, teetering,
      tit for tat, to-and-fro, tottering, train, transposal,
      transposition, undulation, ups and downs, vacillation, variation,
      vicissitude, wavering, wigwag