robin vs Old World robin

robin and Old World robin both are nouns.

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

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

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

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

robin (noun)	Old World robin (noun)
large American thrush having a rust-red breast and abdomen	small Old World songbird with a reddish breast
small Old World songbird with a reddish breast