good deal vs mountain

good deal and mountain both are nouns.

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

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

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

good deal (noun)	mountain (noun)
(often followed by `of') a large number or amount or extent	a land mass that projects well above its surroundings; higher than a hill
	(often followed by `of') a large number or amount or extent