a lot vs unoften

a lot

adv

  • Often; frequently. 

  • Very much; a great deal; to a large extent. 

pron

  • A large amount. 

  • Many things, much. 

unoften

adv

  • seldom, rarely 

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