gray catbird vs grey catbird

gray catbird and grey catbird both are nouns.

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

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

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

Other synonyms of gray catbird include catbird, Dumetella carolinensis.

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