rather vs instead

rather and instead both are adverbs.

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

As adverbs, rather and instead are synonyms defined as:

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