patois vs slang

patois and slang both are nouns.

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

As nouns, patois and slang are synonyms defined as:

patois and slang: a characteristic language of a particular group (as among thieves)

Other synonyms of patois include argot, cant, jargon, lingo, vernacular.

patois (noun)	slang (noun)
a regional dialect of a language (especially French); usually considered substandard	a characteristic language of a particular group (as among thieves)
a characteristic language of a particular group (as among thieves)	informal language consisting of words and expressions that are not considered appropriate for formal occasions; often vituperative or vulgar