1. adjective /ˌɛkstrətɚˈɛstriəl,ˌɛk.stɹə.təˈɹɛst.ɹi.əl/
Originating from outside of the Earths atmosphere, from space, or from another planet; alien to Earth or its environment.
2. noun /ˌɛkstrətɚˈɛstriəl,ˌɛk.stɹə.təˈɹɛst.ɹi.əl/
A being originating from outside of the Earths atmosphere, from space, or from another planet; an alien
See Also: ET
Wikipedia foundation.