Source : Webster's Revised Unabridged Dictionary (1913)

Reversion \Re*ver"sion\, n. [F. r['e]version, L. reversio a
   turning back. See {Revert}.]
   1. The act of returning, or coming back; return. [Obs.]

            After his reversion home, [he] was spoiled, also, of
            all that he brought with him.         --Foxe.

   2. That which reverts or returns; residue. [Obs.]

            The small reversion of this great navy which came
            home might be looked upon by religious eyes as
            relics.                               --Fuller.

   3. (Law) The returning of an esttate to the grantor or his
      heirs, by operation of law, after the grant has
      terminated; hence, the residue of an estate left in the
      proprietor or owner thereof, to take effect in possession,
      by operation of law, after the termination of a limited or
      less estate carved out of it and conveyed by him. --Kent.

   4. Hence, a right to future possession or enjoiment;
      succession.

            For even reversions are all begged before. --Dryden.

   5. (Annuities) A payment which is not to be received, or a
      benefit which does not begin, until the happening of some
      event, as the death of a living person. --Brande &C.

   6. (Biol.) A return towards some ancestral type or character;
      atavism.

   {Reversion of series} (Alg.), the act of reverting a series.
      See {To revert a series}, under {Revert}, v. t.

Source : WordNet®

reversion
     n 1: (law) an interest in an estate that reverts to the grantor
          (or his heirs) at the end of some period (e.g., the
          death of the grantee)
     2: a return to a normal phenotype (usually resulting from a
        second mutation)
     3: a reappearance of an earlier characteristic [syn: {atavism},
         {throwback}]
     4: turning in the opposite direction [syn: {reverse}, {reversal},
         {turnabout}, {turnaround}]
     5: returning to a former state [syn: {regression}, {regress}, {retrogression},
         {retroversion}]
     6: a failure to maintain a higher state [syn: {backsliding}, {lapse},
         {lapsing}, {relapse}, {relapsing}, {reverting}]