grey body vs gray body

grey body and gray body both are nouns.

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

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

grey body and gray body: a body that emits radiation in constant proportion to the corresponding black-body radiation.

grey body (noun)	gray body (noun)
a body that emits radiation in constant proportion to the corresponding black-body radiation.	a body that emits radiation in constant proportion to the corresponding black-body radiation.