rainbow fish vs guppy

rainbow fish and guppy both are nouns.

Word	Noun	Adjective	Verb	Adverb
rainbow fish	Yes	No	No	No
guppy	Yes	No	No	No

As nouns, rainbow fish and guppy are synonyms defined as:

rainbow fish and guppy: small freshwater fish of South America and the West Indies; often kept in aquariums

Other synonyms of rainbow fish include Lebistes reticulatus.

rainbow fish (noun)	guppy (noun)
small freshwater fish of South America and the West Indies; often kept in aquariums	small freshwater fish of South America and the West Indies; often kept in aquariums