: not familiar or like other things you have known : different from what you are used to
: from another country
: too different from something to be acceptable or suitable
: a person who was born in a different country and is not a citizen of the country in which he or she now lives
: a creature that comes from somewhere other than the planet Earth
What made you want to look up alien? Please tell us where you read or heard it (including the quote, if possible).