Source : Webster's Revised Unabridged Dictionary (1913)

Valency \Val"en*cy\, n.; pl. {Valencies}. (Chem.)
   (a) See {Valence}.
   (b) A unit of combining power; a so-called bond of affinity.

Source : WordNet®

valency
     n 1: the phenomenon of forming chemical bonds
     2: (biology) a relative capacity to unite or react or interact
        as with antigens or a biological substrate [syn: {valence}]
     3: (chemistry) a property of atoms or radicals; their combining
        power given in terms of the number of hydrogen atoms (or
        the equivalent) [syn: {valence}]

Source : Free On-Line Dictionary of Computing

valency
     
        See {degree}.