grey catbird vs gray catbird

grey catbird and gray catbird both are nouns.

Word	Noun	Adjective	Verb	Adverb
grey catbird	Yes	No	No	No
gray catbird	Yes	No	No	No

As nouns, grey catbird and gray catbird are synonyms defined as:

grey catbird and gray catbird: North American songbird whose call resembles a cat's mewing

Other synonyms of grey catbird include catbird, Dumetella carolinensis.

grey catbird (noun)	gray catbird (noun)
North American songbird whose call resembles a cat's mewing	North American songbird whose call resembles a cat's mewing