Ethereal, a.
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; characterized by extreme delicacy, as form, manner, thought, etc. Vast chain of being, which from God began, Natures ethereal, human, angel, man. Pope.
3. (Chem.)
Pertaining to, derived from, or resembling, ether; as, ethereal salts. Ethereal oil. (Chem.) See Essential oil, under Essential. -- Ethereal oil of wine (Chem.), a heavy, yellow, oily liquid consisting essentially of etherin, etherol, and ethyl sulphate. It is the oily residuum left after etherification. Called also heavy oil of wine (distinguished from oil of wine, or oenanthic ether). -- Ethereal salt (Chem.), a salt of some organic radical as a base; an ester.
Shades of meaning
Fernald has no entry of its own for ethereal; he lists it under airy.
Where he writes about it:
Aerial and airy both signify of or belonging to the air, but airy also describes that which seems as if made of air; we speak of airy shapes, airy nothings, where we could not well say aerial; ethereal describes its object as belonging to the upper air, the pure ether, and so, often, heavenly. — from airy