digression vs variation

digression

noun
  • An elongation, a deflection or deviation from a mean position or expected path. 

  • An aside, an act of straying from the main subject in speech or writing. 

  • The act of straying from the main subject in speech or writing, (rhetoric) particularly for rhetorical effect. 

variation

noun
  • Deviation from the mean orbit of a heavenly body. 

  • The act of varying; a partial change in the form, position, state, or qualities of a thing. 

  • The angular difference at the vessel between the direction of true north and magnetic north. 

  • A related but distinct thing. 

  • A line of play that differs from the original. 

  • The modification of a hereditary trait. 

  • A technique where material is repeated with alterations to the melody, harmony, rhythm, timbre, texture, counterpoint or orchestration; but with some invariant characteristic, e.g. a ground bass. 

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