Source : Webster's Revised Unabridged Dictionary (1913)

Relatedness \Re*lat"ed*ness\, n.
   The state or condition of being related; relationship;
   affinity. [R.] --Emerson.

Source : WordNet®

relatedness
     n : a particular manner of connectedness; "the relatedness of
         all living things" [ant: {unrelatedness}]