fish tank vs fish bowl

fish tank and fish bowl both are nouns.

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

As nouns, fish bowl is a hyponym of fish tank; that is, fish bowl is a word with a more specific, narrower meaning than fish tank:

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

Other hyponyms of fish tank include fishbowl, goldfish bowl.

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