adumbrate vs darken

adumbrate

verb
  • To obscure or overshadow. 

  • To foreshadow vaguely. 

  • To give a vague outline. 

darken

verb
  • To cloud, obscure, or perplex; to render less clear or intelligible. 

  • To become gloomy, darker in mood. 

  • To render gloomy, darker in mood. 

  • To become dark or darker (having less light). 

  • To make dark or darker by reducing light. 

  • To make dark or darker in colour. 

  • To blind, impair the eyesight. 

  • To become dark or darker in colour. 

  • To be blinded, lose one’s eyesight. 

  • To make foul; to sully; to tarnish. 

  • To get dark (referring to the sky, either in the evening or as a result of cloud). 

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