'Similarity' definitions:

Definition of 'similarity'

From: WordNet
noun
The quality of being similar [ant: dissimilarity, unsimilarity]
noun
A Gestalt principle of organization holding that (other things being equal) parts of a stimulus field that are similar to each other tend to be perceived as belonging together as a unit [syn: similarity, law of similarity]

Definition of 'Similarity'

From: GCIDE
  • Similarity \Sim`i*lar"i*ty\, n.; pl. -ties. [Cf. F. similarit['e].] The quality or state of being similar; likeness; resemblance; as, a similarity of features. [1913 Webster]
  • Hardly is there a similarity detected between two or three facts, than men hasten to extend it to all. --Sir W. Hamilton. [1913 Webster]