approximate vs make a guess at

approximate

adj
  • Nearing correctness; nearly exact; not perfectly accurate. 

  • Approaching; proximate; nearly resembling. 

verb
  • To come near to; to approach. 

  • To carry or advance near; to cause to approach. 

  • To estimate. 

make a guess at

How often have the words approximate and make a guess at occurred in a corpus of books? (source: Google Ngram Viewer )