redbreast vs Old World robin

redbreast and Old World robin both are nouns.

Word	Noun	Adjective	Verb	Adverb
redbreast	Yes	No	No	No
Old World robin	Yes	No	No	No

As nouns, redbreast and Old World robin are synonyms defined as:

redbreast and Old World robin: small Old World songbird with a reddish breast

Other synonyms of redbreast include Erithacus rubecola, robin, robin redbreast.

redbreast (noun)	Old World robin (noun)
small Old World songbird with a reddish breast	small Old World songbird with a reddish breast