gr. αιθήρ, aithêr: éter. Trata-se do éter, este corpo eterno, inalterável e imapssível do qual se compõe o céu. O éter não sofre por natureza nenhum corrimento. Sendo composto de éter, o corpo dos astros permanece então perfeitamente imutável.
“Ether.” In early Greek thought, including the poets, aither is the purer air breathed by the Gods on the mountaintops or the realm of light in the heavens. For Aristotle, aither is the “fifth element” after earth, water, air, and fire; it is the material substrate of astronomical entities, and it naturally moves in a circle. It is also, for Aristotle , the medium for the transmission of light. And he suggests some sort of affinity between aither and pneuma, the special material instrument of the soul (psyche) in his Generation and Movement of Animals (GA II .6). (HDAGP)