乙醚又称依打（Ether音译）、二乙醚或乙氧基乙烷，是一种醚类，分子式为 (C₂H₅)₂O (或简写为 Et₂O)。乙醚是一种无色、易燃、极易挥发的液体，其气味带有刺激性，以前被当作吸入性全身麻醉剂，也是常见的毒品。乙醚亦是一种用途非常广泛的极性有机溶剂，与空气隔绝时相当稳定。乙醚蒸气能与空气形成爆炸性混合物，当它遇到火花、高温、氧化剂（如高氯酸、氯气、氧气、臭氧等）时，就有发生燃烧爆炸的危险，有时也因静电而起火。略溶于水，能溶于乙醇、苯、氯仿、石油醚、其它极性溶液及许多油类，也可以提炼青蒿素。

Diethyl ether, also known as ethoxyethane, ethyl ether, sulfuric ether, or simply ether, is an organic compound in the ether class with the formula (C
2H
5)
2O. It is a colorless, highly volatile flammable liquid. It is commonly used as a solvent and was once used as a general anesthetic. It has narcotic properties and has been known to cause temporary dependence, the only symptom of which is the will to consume more, sometimes referred to as etheromania.