noun
a being from another planet or world; extraterrestrial
adjective
belonging to a foreign country or nation; unfamiliar and disturbing or distasteful
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The scientist claimed to have discovered evidence of an alien presence on the distant planet.
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I heard a rumor that there are aliens living among us.
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Dude, do you believe in aliens and UFOs?
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Her ideas were so innovative, they seemed almost alien to the traditional way of thinking.