ethereal vs imponderable

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. 

imponderable

adj
  • Not ponderable; without sensible or appreciable weight; incapable of being weighed. 

  • Difficult or impossible to comprehend or evaluate. 

noun
  • An imponderable question. 

  • A factor that cannot be anticipated. 

  • An imponderable substance or body; specifically, in the plural, a name formerly applied to heat, light, electricity, and magnetism. 

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