protist vs microorganism

protist and microorganism both are nouns.

Word	Noun	Adjective	Verb	Adverb
protist	Yes	No	No	No
microorganism	Yes	No	No	No

As nouns, microorganism is a hypernym of protist; that is, microorganism is a word with a broader meaning than protist:

protist: free-living or colonial organisms with diverse nutritional and reproductive modes
microorganism: any organism of microscopic size

Other hypernyms of protist include micro-organism.

protist (noun)	microorganism (noun)
free-living or colonial organisms with diverse nutritional and reproductive modes	any organism of microscopic size