living thing vs unit

living thing and unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
living thing	Yes	No	No	No
unit	Yes	No	No	No

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

Other hypernyms of living thing include whole.

living thing (noun)	unit (noun)
a living (or once living) entity	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