activity vs task

activity

noun
  • Something done as an action or a movement. 

  • The lexical aspect (aktionsart) of verbs or predicates that change over time and have no natural end point. 

  • Something done for pleasure or entertainment, especially one involving movement or an excursion. 

  • The state or quality of being active; activeness. 

  • The number of radioactive decays per unit time. Unit for it: becquerel or curie 

  • The propery of substances to react with other substances 

task

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

  • Any piece of work done. 

  • A difficult or tedious undertaking. 

  • A process or execution of a program. 

  • An objective. 

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 

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