extraterrestrialPronunciation: /ˌɛkstrətəˈrɛstrɪəl/Translate extraterrestrial | into French | into Italian Definition of extraterrestrial adjective of or from outside the earth or its atmosphere:searches for extraterrestrial intelligence noun a hypothetical or fictional being from outer space. extraterrestrial in other Oxford dictionaries Definition of extraterrestrial in the US English dictionary