similar vs synonymous

similar

adj
  • Having traits or characteristics in common; alike, comparable. 

  • Of geometrical figures including triangles, squares, ellipses, arcs and more complex figures, having the same shape but possibly different size, rotational orientation, and position; in particular, having corresponding angles equal and corresponding line segments proportional; such that one can be had from the other using a sequence of rotations, translations and scalings. 

  • Of two square matrices; being such that a conjugation sends one matrix to the other. 

noun
  • That which is similar to, or resembles, something else, as in quality, form, etc. 

  • A material that produces an effect that resembles the symptoms of a particular disease. 

synonymous

adj
  • Having an identical meaning. 

  • Having a similar meaning. 

  • Such that both its forms yield the same sequenced protein. 

  • Of, or being a synonym. 

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