congruence vs similarity

congruence

noun
  • Matrix similarity by an orthogonal matrix. 

  • The quality of agreeing or corresponding; being suitable and appropriate. 

  • A relation between two numbers indicating they give the same remainder when divided by some given number. 

  • More generally: any equivalence relation defined on an algebraic structure which is preserved by operations defined by the structure. 

  • The quality of being isometric — roughly, the same measure and shape. 

similarity

noun
  • The property of two matrices being similar. 

  • A transformation that preserves angles and the ratios of distances 

  • Closeness of appearance to something else. 

  • The relation of sharing properties. 

How often have the words congruence and similarity occurred in a corpus of books? (source: Google Ngram Viewer )