fish tank vs fishbowl

fish tank and fishbowl both are nouns.

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

As nouns, fishbowl is a hyponym of fish tank; that is, fishbowl 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
fishbowl: a transparent bowl in which small fish are kept

Other hyponyms of fish tank include fish bowl, goldfish bowl.

fish tank (noun)	fishbowl (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