instead vs rather

instead and rather both are adverbs.

Word	Noun	Adjective	Verb	Adverb
instead	No	No	No	Yes
rather	No	No	No	Yes

As adverbs, instead and rather are synonyms defined as:

instead (adverb)	rather (adverb)
in place of, or as an alternative to	to a degree (not used with a negative)
on the contrary	more readily or willingly
	on the contrary
	to some (great or small) extent