unit vs living thing

unit and living thing both are nouns.

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

As nouns, living thing is a hyponym of unit; that is, living thing is a word with a more specific, narrower meaning than unit:

unit (noun)	living thing (noun)
an assemblage of parts that is regarded as a single entity	a living (or once living) 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