dunce cap vs dunce's cap

dunce cap and dunce's cap both are nouns.

Word	Noun	Adjective	Verb	Adverb
dunce cap	Yes	No	No	No
dunce's cap	Yes	No	No	No

As nouns, dunce cap and dunce's cap are synonyms defined as:

dunce cap and dunce's cap: a cone-shaped paper hat formerly placed on the head of slow or lazy pupils

Other synonyms of dunce cap include fool's cap.

dunce cap (noun)	dunce's cap (noun)
a cone-shaped paper hat formerly placed on the head of slow or lazy pupils	a cone-shaped paper hat formerly placed on the head of slow or lazy pupils