instead vs rather

instead

adv
  • In the place of something (usually mentioned earlier); as a substitute or alternative. 

rather

adv
  • Used to specify a choice or preference; preferably, in preference to. (Now usually followed by than) 

  • Used to introduce a contradiction; on the contrary. 

  • Somewhat, fairly. 

  • Introducing a qualification or clarification; more precisely. (Now usually preceded by or.) 

verb
  • To prefer; to prefer to. 

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