pigeon breast vs malformation

pigeon breast and malformation both are nouns.

Word	Noun	Adjective	Verb	Adverb
pigeon breast	Yes	No	No	No
malformation	Yes	No	No	No

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

pigeon breast: abnormal protrusion of the breastbone caused by rickets
malformation: an affliction in which some part of the body is misshapen or malformed

Other hypernyms of pigeon breast include deformity, misshapenness.

pigeon breast (noun)	malformation (noun)
abnormal protrusion of the breastbone caused by rickets	something abnormal or anomalous
	an affliction in which some part of the body is misshapen or malformed