The Collaborative International Dictionary of English v.0.48:

Basicity \Ba*sic"i*ty\, n. (Chem.)
   (a) The quality or state of being a base.
   (b) The power of an acid to unite with one or more atoms or
       equivalents of a base, as indicated by the number of
       replaceable hydrogen atoms contained in the acid.
       [1913 Webster]