alien vs foreigner

alien and foreigner both are nouns.

Word	Noun	Adjective	Verb	Adverb
alien	Yes	Yes	Yes	No
foreigner	Yes	No	No	No

As nouns, alien and foreigner are synonyms defined as:

alien and foreigner: a person who comes from a foreign country; someone who does not owe allegiance to your country

Other synonyms of alien include noncitizen, outlander.

As nouns, foreigner is a hyponym of alien; that is, foreigner is a word with a more specific, narrower meaning than alien:

alien: anyone who does not belong in the environment in which they are found
foreigner: someone who is excluded from or is not a member of a group

Other hyponyms of alien include outsider.

alien (noun)	foreigner (noun)
a person who comes from a foreign country; someone who does not owe allegiance to your country	a person who comes from a foreign country; someone who does not owe allegiance to your country
anyone who does not belong in the environment in which they are found	someone who is excluded from or is not a member of a group
a form of life assumed to exist outside the Earth or its atmosphere

alien (adjective)	foreigner (adjective)
not contained in or deriving from the essential nature of something
being or from or characteristic of another place or part of the world

alien (verb)	foreigner (verb)
transfer property or ownership