gefilte fish vs fish ball

gefilte fish and fish ball both are nouns.

Word	Noun	Adjective	Verb	Adverb
gefilte fish	Yes	No	No	No
fish ball	Yes	No	No	No

As nouns, gefilte fish and fish ball are synonyms defined as:

gefilte fish and fish ball: well-seasoned balls of ground fish and eggs and crushed crumbs simmered in fish stock

gefilte fish (noun)	fish ball (noun)
well-seasoned balls of ground fish and eggs and crushed crumbs simmered in fish stock	well-seasoned balls of ground fish and eggs and crushed crumbs simmered in fish stock
	a fried ball or patty of flaked fish and mashed potatoes