folk vs rabble

folk and rabble both are nouns.

Word	Noun	Adjective	Verb	Adverb
folk	Yes	No	No	No
rabble	Yes	No	No	No

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

folk (noun)	rabble (noun)
the traditional and typically anonymous music that is an expression of the life of people in a community	a disorderly crowd of people
people in general (often used in the plural)	disparaging terms for the common people
a social division of (usually preliterate) people
people descended from a common ancestor