acclivity vs decline

acclivity

noun
  • A slope or inclination of the earth, as the side of a hill, considered as ascending, in opposition to declivity, or descending; an upward slope; ascent. 

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). 

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