good deal vs plenty

good deal and plenty both are nouns.

Word	Noun	Adjective	Verb	Adverb
good deal	Yes	No	No	No
plenty	Yes	No	No	Yes

As nouns, good deal and plenty are synonyms defined as:

good deal and plenty: (often followed by `of') a large number or amount or extent

good deal (noun)	plenty (noun)
(often followed by `of') a large number or amount or extent	a full supply
	(often followed by `of') a large number or amount or extent

good deal (adverb)	plenty (adverb)
	as much as necessary