Source : Webster's Revised Unabridged Dictionary (1913)

Equivalence \E*quiv"a*lence\, n. [Cf. F. ['e]quivalence, LL.
   aequivalentia.]
   1. The condition of being equivalent or equal; equality of
      worth, value, signification, or force; as, an equivalence
      of definitions.

   2. Equal power or force; equivalent amount.

   3. (Chem.)
      (a) The quantity of the combining power of an atom,
          expressed in hydrogen units; the number of hydrogen
          atoms can combine with, or be exchanged for; valency.
          See {Valence}.
      (b) The degree of combining power as determined by
          relative weight. See {Equivalent}, n., 2. [R.]

Equivalence \E*quiv"a*lence\, v. t.
   To be equivalent or equal to; to counterbalance. [R.] --Sir
   T. Browne.

Source : WordNet®

equivalence
     n 1: a state of being essentially equal or equivalent; equally
          balanced; "on a par with the best" [syn: {equality}, {equation},
           {par}]
     2: essential equality and interchangeability [ant: {nonequivalence}]
     3: qualities that are comparable; "no comparison between the
        two books"; "beyond compare" [syn: {comparison}, {compare},
         {comparability}]