E*quiv"a*lence (?), n. [Cf. F. équivalence, 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.]

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

• the condition of being equivalent or essentially equal
  
• (mathematics) an equivalence relation
  
• (logic) the relationship between two propositions that are either both true or both false