protistan vs micro-organism

protistan and micro-organism both are nouns.

Word	Noun	Adjective	Verb	Adverb
protistan	Yes	No	No	No
micro-organism	Yes	No	No	No

As nouns, micro-organism is a hypernym of protistan; that is, micro-organism is a word with a broader meaning than protistan:

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

Other hypernyms of protistan include microorganism.

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