Aether is an old way of spelling ether when it means the air or the sky, especially the bright high air the old Greeks thought of as a kind of pure sky-stuff above the clouds. Poets and old science books keep this spelling; everyday English now writes ether, and even that sense feels literary. Though actually the word has worn several coats. Ancient thinkers treated aether as a fifth element, not earth, water, air, or fire. Much later, scientists used it for an invisible something they thought light needed in order to travel — and then that idea was dropped. The chemical liquid called ether (the sharp-smelling one that once put people to sleep for operations) is a different use, and many students meet that one first. This entry is the sky and air word, in its older clothes. From Greek aithēr, upper air; the god Ether is a doublet — same old name, different job.