goldfish bowl vs fish tank

goldfish bowl and fish tank both are nouns.

Word	Noun	Adjective	Verb	Adverb
goldfish bowl	Yes	No	No	No
fish tank	Yes	No	No	No

As nouns, fish tank is a hypernym of goldfish bowl; that is, fish tank is a word with a broader meaning than goldfish bowl:

goldfish bowl: a transparent bowl in which small fish are kept
fish tank: a tank or pool or bowl filled with water for keeping live fish and underwater animals

Other hypernyms of goldfish bowl include aquarium, marine museum, bowl.

goldfish bowl (noun)	fish tank (noun)
a transparent bowl in which small fish are kept	a tank or pool or bowl filled with water for keeping live fish and underwater animals
a state of affairs in which you have no privacy