opportunism vs selfishness

opportunism and selfishness both are nouns.

Word	Noun	Adjective	Verb	Adverb
opportunism	Yes	No	No	No
selfishness	Yes	No	No	No

As nouns, selfishness is a hypernym of opportunism; that is, selfishness is a word with a broader meaning than opportunism:

opportunism: taking advantage of opportunities without regard for the consequences for others
selfishness: stinginess resulting from a concern for your own welfare and a disregard of others

opportunism (noun)	selfishness (noun)
taking advantage of opportunities without regard for the consequences for others	stinginess resulting from a concern for your own welfare and a disregard of others