macrocephaly vs abnormalcy

macrocephaly and abnormalcy both are nouns.

Word	Noun	Adjective	Verb	Adverb
macrocephaly	Yes	No	No	No
abnormalcy	Yes	No	No	No

As nouns, abnormalcy is a hypernym of macrocephaly; that is, abnormalcy is a word with a broader meaning than macrocephaly:

macrocephaly: an abnormally large head; differs from hydrocephalus because there is no increased intracranial pressure and the overgrowth is symmetrical
abnormalcy: an abnormal physical condition resulting from defective genes or developmental deficiencies

Other hypernyms of macrocephaly include abnormality.

macrocephaly (noun)	abnormalcy (noun)
an abnormally large head; differs from hydrocephalus because there is no increased intracranial pressure and the overgrowth is symmetrical	an abnormal physical condition resulting from defective genes or developmental deficiencies