pirate flag vs Jolly Roger

pirate flag and Jolly Roger both are nouns.

Word	Noun	Adjective	Verb	Adverb
pirate flag	Yes	No	No	No
Jolly Roger	Yes	No	No	No

As nouns, pirate flag and Jolly Roger are synonyms defined as:

pirate flag and Jolly Roger: a flag usually bearing a white skull and crossbones on a black background; indicates a pirate ship

Other synonyms of pirate flag include black flag, blackjack.

pirate flag (noun)	Jolly Roger (noun)
a flag usually bearing a white skull and crossbones on a black background; indicates a pirate ship	a flag usually bearing a white skull and crossbones on a black background; indicates a pirate ship