half-bred vs half-breed

half-bred is not a noun while half-breed is a noun.

Word	Noun	Adjective	Verb	Adverb
half-bred	No	Yes	No	No
half-breed	Yes	Yes	No	No

As adjectives, half-bred and half-breed are synonyms defined as:

Other synonyms of half-bred include half-blooded.

half-bred (noun)	half-breed (noun)
	an offensive term for an offspring of parents of different racial group (especially of Caucasian and American Indian ancestry)

half-bred (adjective)	half-breed (adjective)
(of animals) having only one purebred parent	(of animals) having only one purebred parent