ethereal vs evanescent

ethereal

adj
  • Consisting of ether; hence, exceedingly light or airy; tenuous; spiritlike; characterized by extreme delicacy, as form, manner, thought, etc. 

  • Pertaining to the (real or hypothetical) upper, purer air, or to the higher regions beyond the earth or beyond the atmosphere. 

  • To do with diethyl ether. 

  • Pertaining to the immaterial realm, as symbolically represented by, or (in earlier epochs) conflated with, such atmospheric and extra-atmospheric concepts. 

evanescent

adj
  • Ephemeral, fleeting, momentary. 

  • Disappearing, vanishing. 

  • Of an oscillating electric or magnetic field: not propagating as an electromagnetic wave but having its energy spatially concentrated in the vicinity of its source. 

  • Of a number or value: diminishing to the point of reaching zero as a limit; infinitesimal. 

  • Of plant parts: shed after a period. 

  • Barely there; almost imperceptible. 

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