outsider vs stranger

outsider and stranger both are nouns.

Word	Noun	Adjective	Verb	Adverb
outsider	Yes	No	No	No
stranger	Yes	No	No	No

As nouns, stranger is a hypernym of outsider; that is, stranger is a word with a broader meaning than outsider:

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

Other hypernyms of outsider include alien, unknown.

outsider (noun)	stranger (noun)
someone who is excluded from or is not a member of a group	anyone who does not belong in the environment in which they are found
a contestant (human or animal) not considered to have a good chance to win	an individual that one is not acquainted with