macrencephaly vs abnormalcy

macrencephaly and abnormalcy both are nouns.

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

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

macrencephaly: an abnormally large braincase
abnormalcy: an abnormal physical condition resulting from defective genes or developmental deficiencies

Other hypernyms of macrencephaly include abnormality.

macrencephaly (noun)	abnormalcy (noun)
an abnormally large braincase	an abnormal physical condition resulting from defective genes or developmental deficiencies