hebetate vs slacken

hebetate

verb
  • To render obtuse; to dull; to blunt. 

adj
  • obtuse; dull 

  • Having a dull or blunt and soft point 

slacken

verb
  • To make slack, less taut, or less intense. 

  • To gradually decrease in intensity or tautness; to become slack. 

  • To deprive of cohesion by combining chemically with water; to slake. 

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