pouter pigeon vs pigeon

pouter pigeon and pigeon both are nouns.

Word	Noun	Adjective	Verb	Adverb
pouter pigeon	Yes	No	No	No
pigeon	Yes	No	No	No

As nouns, pigeon is a hypernym of pouter pigeon; that is, pigeon is a word with a broader meaning than pouter pigeon:

pouter pigeon: one of a breed of pigeon that enlarge their crop until their breast is puffed out
pigeon: wild and domesticated birds having a heavy body and short legs

pouter pigeon (noun)	pigeon (noun)
one of a breed of pigeon that enlarge their crop until their breast is puffed out	wild and domesticated birds having a heavy body and short legs