affine vs lighten

affine

verb
  • To refine. 

noun
  • A relative by marriage. 

adj
  • Of or pertaining to a function expressible as f(⃑x)=A⃑x+⃑b (where A is a linear transformation and ⃑b is a constant), which, regarded as a transformation, maps parallel lines to parallel lines and finite points to finite points. 

  • Assigning finite values to finite quantities. 

  • Of two materials, having mutual affinity. 

lighten

verb
  • To alleviate; to reduce the burden of. 

  • To become light or lighter in weight. 

  • To become brighter or clearer; to brighten. 

  • To make less serious or more cheerful. 

  • To illuminate with knowledge; to enlighten. 

  • To descend; to light. 

  • To emit or disclose in, or as if in, lightning; to flash out, like lightning. 

  • To become less serious or more cheerful. 

  • To make brighter or clearer; to illuminate. 

  • To make light or lighter in weight. 

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