kind of vs rather

kind of and rather both are adverbs.

Word	Noun	Adjective	Verb	Adverb
kind of	No	No	No	Yes
rather	No	No	No	Yes

As adverbs, kind of and rather are synonyms defined as:

Other synonyms of kind of include kinda, sort of.

kind of (adverb)	rather (adverb)
to some (great or small) extent	to a degree (not used with a negative)
	more readily or willingly
	on the contrary
	to some (great or small) extent