Muslim vs Sunni Muslim

Muslim and Sunni Muslim both are nouns.

Word	Noun	Adjective	Verb	Adverb
Muslim	Yes	Yes	No	No
Sunni Muslim	Yes	No	No	No

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

Muslim: a believer in or follower of Islam
Sunni Muslim: a member of the branch of Islam that accepts the first four caliphs as rightful successors to Muhammad

Muslim (noun)	Sunni Muslim (noun)
a believer in or follower of Islam	a member of the branch of Islam that accepts the first four caliphs as rightful successors to Muhammad

Muslim (adjective)	Sunni Muslim (adjective)
of or relating to or supporting Islamism