dialect vs patois

dialect and patois both are nouns.

Word	Noun	Adjective	Verb	Adverb
dialect	Yes	No	No	No
patois	Yes	No	No	No

As nouns, patois is a hyponym of dialect; that is, patois is a word with a more specific, narrower meaning than dialect:

dialect: the usage or vocabulary that is characteristic of a specific group of people
patois: a regional dialect of a language (especially French); usually considered substandard

Other hyponyms of dialect include eye dialect.

dialect (noun)	patois (noun)
the usage or vocabulary that is characteristic of a specific group of people	a regional dialect of a language (especially French); usually considered substandard
	a characteristic language of a particular group (as among thieves)