natural object vs unit

natural object and unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
natural object	Yes	No	No	No
unit	Yes	No	No	No

As nouns, unit is a hypernym of natural object; that is, unit is a word with a broader meaning than natural object:

Other hypernyms of natural object include whole.

natural object (noun)	unit (noun)
an object occurring naturally; not made by man	an assemblage of parts that is regarded as a single entity
	a single undivided whole
	an organization regarded as part of a larger social group
	a single undivided natural thing occurring in the composition of something else
	any division of quantity accepted as a standard of measurement or exchange
	an individual or group or structure or other entity regarded as a structural or functional constituent of a whole