fluctuation vs similarity

fluctuation

noun
  • A wavering; unsteadiness. 

  • In medicine, a wave-like motion or undulation of a fluid in a natural or abnormal cavity (e.g. pus in an abscess), which is felt during palpation or percussion. 

  • A motion like that of waves; a moving in this and that direction. 

similarity

noun
  • A transformation that preserves angles and the ratios of distances 

  • The property of two matrices being similar. 

  • Closeness of appearance to something else. 

  • The relation of sharing properties. 

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