cardiomegaly vs symptom

cardiomegaly and symptom both are nouns.

Word	Noun	Adjective	Verb	Adverb
cardiomegaly	Yes	No	No	No
symptom	Yes	No	No	No

As nouns, symptom is a hypernym of cardiomegaly; that is, symptom is a word with a broader meaning than cardiomegaly:

cardiomegaly: an abnormal enlargement of the heart
symptom: (medicine) any sensation or change in bodily function that is experienced by a patient and is associated with a particular disease

cardiomegaly (noun)	symptom (noun)
an abnormal enlargement of the heart	anything that accompanies X and is regarded as an indication of X's existence
	(medicine) any sensation or change in bodily function that is experienced by a patient and is associated with a particular disease