unit vs assembly

unit and assembly both are nouns.

Word	Noun	Adjective	Verb	Adverb
unit	Yes	No	No	No
assembly	Yes	No	No	No

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

unit (noun)	assembly (noun)
an assemblage of parts that is regarded as a single entity	the social act of assembling
a single undivided whole	the act of constructing something (as a piece of machinery)
an organization regarded as part of a larger social group	a group of machine parts that fit together to form a self-contained unit
a single undivided natural thing occurring in the composition of something else	a public facility to meet for open discussion
any division of quantity accepted as a standard of measurement or exchange	a unit consisting of components that have been fitted together
an individual or group or structure or other entity regarded as a structural or functional constituent of a whole	a group of persons who are gathered together for a common purpose