Jolly Roger vs black flag

Jolly Roger and black flag both are nouns.

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

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

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

Other synonyms of Jolly Roger include blackjack, pirate flag.

Jolly Roger (noun)	black 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