task vs thing to be done

task

verb
  • To charge, as with a fault. 

  • To assign a task to, or impose a task on. 

  • To oppress with severe or excessive burdens; to tax 

noun
  • Any piece of work done. 

  • A difficult or tedious undertaking. 

  • A process or execution of a program. 

  • An objective. 

  • A piece of work done as part of one’s duties. 

thing to be done

How often have the words task and thing to be done occurred in a corpus of books? (source: Google Ngram Viewer )