The Collaborative International Dictionary of English v.0.48:

Sameness \Same"ness\, n.
   1. The state of being the same; identity; absence of
      difference; near resemblance; correspondence; similarity;
      as, a sameness of person, of manner, of sound, of
      appearance, and the like. "A sameness of the terms." --Bp.
      Horsley.
      [1913 Webster]

   2. Hence, want of variety; tedious monotony.
      [1913 Webster]

   Syn: Identity; identicalness; oneness.
        [1913 Webster]

WordNet (r) 3.0 (2006):

sameness
    n 1: the quality of being alike; "sameness of purpose kept them
         together" [ant: difference]
    2: the quality of wearisome constancy, routine, and lack of
       variety; "he had never grown accustomed to the monotony of
       his work"; "he was sick of the humdrum of his fellow
       prisoners"; "he hated the sameness of the food the college
       served" [syn: monotony, humdrum, sameness]