Source : Webster's Revised Unabridged Dictionary (1913)

Linkage \Link"age\ (l[i^][ng]k"[asl]j; 48), n.
   1. The act of linking; the state of being linked; also, a
      system of links.

   2. (Chem.) Manner of linking or of being linked; -- said of
      the union of atoms or radicals in the molecule.

   3. (Geom.) A system of straight lines or bars, fastened
      together by joints, and having certain of their points
      fixed in a plane. It is used to describe straight lines
      and curves in the plane.

Source : WordNet®

linkage
     n 1: an associative relation
     2: (genetics) traits that tend to be inherited together as a
        consequence of an association between their genes; all of
        the genes of a given chromosome are linked (where one goes
        they all go) [syn: {gene linkage}]
     3: a mechanical system of rods or springs or pivots that
        transmits power or motion
     4: the act of linking things together