sever vs work in

sever

verb
  • To make a separation or distinction; to distinguish. 

  • To disconnect; to disunite; to terminate. 

  • To cut free. 

  • To suffer disjunction; to be parted or separated. 

work in

verb
  • Used other than figuratively or idiomatically: see work, in. 

  • To find time or space for, amid other things. 

  • To work out using a machine in between the sets of someone who is already using that machine. 

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