slang vs patois

slang and patois both are nouns.

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

As nouns, slang and patois are synonyms defined as:

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

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

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