unit vs combination

unit and combination both are nouns.

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

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

unit (noun)	combination (noun)
an assemblage of parts that is regarded as a single entity	the act of combining things to form a new whole
a single undivided whole	the act of arranging elements into specified groups without regard to order
an organization regarded as part of a larger social group	a collection of things that have been combined; an assemblage of separate parts or qualities
a single undivided natural thing occurring in the composition of something else	a group of people (often temporary) having a common purpose
any division of quantity accepted as a standard of measurement or exchange	a sequence of numbers or letters that opens a combination lock
an individual or group or structure or other entity regarded as a structural or functional constituent of a whole	an alliance of people or corporations or countries for a special purpose (formerly to achieve some antisocial end but now for general political or economic purposes)
	a coordinated sequence of chess moves