selflessness vs unselfishness

selflessness and unselfishness both are nouns.

Word	Noun	Adjective	Verb	Adverb
selflessness	Yes	No	No	No
unselfishness	Yes	No	No	No

As nouns, unselfishness is a hypernym of selflessness; that is, unselfishness is a word with a broader meaning than selflessness:

selflessness: the quality of unselfish concern for the welfare of others
unselfishness: the quality of not putting yourself first but being willing to give your time or money or effort etc. for others

selflessness (noun)	unselfishness (noun)
acting with less concern for yourself than for the success of the joint activity	acting generously
the quality of unselfish concern for the welfare of others	the quality of not putting yourself first but being willing to give your time or money or effort etc. for others