1. Pertaining to the hypothetical upper, purer air, or to the higher regions beyond the earth or beyond the atmosphere; celestial; as, ethereal space; ethereal regions. Go, heavenly guest, ethereal messenger. (Milton)
2. Consisting of ether; hence, exceedingly light or airy; tenuous; spiritlike; characterised by extreme delicacy, as form, manner, thought, etc. Vast chain of being, which from god began, natures ethereal, human, angel, man. (Pope)
3. (Science: chemistry) Pertaining to, derived from, or resembling, ether; as, ethereal salts. Ethereal oil.
(Science: chemistry) a salt of some organic radical as a base; an ester.