fish tank vs aquarium

fish tank and aquarium both are nouns.

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

As nouns, fish tank and aquarium are synonyms defined as:

fish tank and aquarium: a tank or pool or bowl filled with water for keeping live fish and underwater animals

Other synonyms of fish tank include marine museum.

fish tank (noun)	aquarium (noun)
a tank or pool or bowl filled with water for keeping live fish and underwater animals	a tank or pool or bowl filled with water for keeping live fish and underwater animals