decline vs drop-off

decline

noun
  • A sloping downward, e.g. of a hill or road. 

  • A weakening. 

  • Downward movement, fall. 

  • A reduction or diminution of activity. 

  • The act of declining or refusing something. 

verb
  • To choose not to do something; refuse, forbear, refrain. 

  • To run through from first to last; to recite in order as though declining a noun. 

  • To cause to decrease or diminish. 

  • To bend downward; to bring down; to depress; to cause to bend, or fall. 

  • To turn or bend aside; to deviate; to stray; to withdraw. 

  • To move downwards, to fall, to drop. 

  • To inflect for case, number, gender, and the like. 

  • To reject a penalty against the opposing team, usually because the result of accepting it would benefit the non-penalized team less than the preceding play. 

  • To become weaker or worse. 

  • To recite all the different declined forms of (a word). 

drop-off

noun
  • A sudden downward slope. 

  • A delivery; the act of leaving a package, etc. 

  • A visitor to a website who ceases to continue using and navigating around the site after reaching some specified page; or such an act of cessation. 

  • The precipitous outer side of a coral reef, facing the open sea. 

  • A sudden decrease. 

  • A space reserved outside a bus or railway station for vehicles stopping to drop off passengers for onward transit. 

  • A time during which passengers, such as school children, are dropped off. 

How often have the words decline and drop-off occurred in a corpus of books? (source: Google Ngram Viewer )