The word Alien does not only mean a creature or being from outer space, another world, galaxy, universe or dimension. As is portrayed by popular science fiction movies. Just like every English word it has more than one meaning and a history behind it. Alien = a person who has not been given the legal right to reside in a new country, or is a person that a particular government considers to be a person sympathetic to a current enemy state. it has particular relevance to American English because it is tied up with law "the immigration and aliens act" that is two hundred years old and has had several changes. So in essence an alien is just another word for a foreigner and the two words "foreigner" and "alien" can be used interchangeably. Related words are "extra" "terrestrial" and "extraterrestrial". Also you can say that something is "alien to you" to mean it is strange and unknown or foreign to you. And in its adjective form you can become alienated from something or someone. Increase your vocabulary and learn how to use the different words in English for different contexts. An alien today and alienated, but a friend and brother or sister tomorrow. English is always changing.