Jolly Roger vs pirate flag

Jolly Roger and pirate flag both are nouns.

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

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

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

Other synonyms of Jolly Roger include black flag, blackjack.

Jolly Roger (noun)	pirate flag (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