microorganism vs organism

microorganism and organism both are nouns.

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

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

microorganism: any organism of microscopic size
organism: a living thing that has (or can develop) the ability to act or function independently

Other hypernyms of microorganism include being.

microorganism (noun)	organism (noun)
any organism of microscopic size	a living thing that has (or can develop) the ability to act or function independently
	a system considered analogous in structure or function to a living body