baldness vs alopecia

baldness and alopecia both are nouns.

Word	Noun	Adjective	Verb	Adverb
baldness	Yes	No	No	No
alopecia	Yes	No	No	No

As nouns, alopecia is a hyponym of baldness; that is, alopecia is a word with a more specific, narrower meaning than baldness:

baldness: the condition of having no hair on the top of the head
alopecia: loss of hair (especially on the head) or loss of wool or feathers; in humans it can result from heredity or hormonal imbalance or certain diseases or drugs and treatments (chemotherapy for cancer)

Other hyponyms of baldness include male-patterned baldness, male pattern baldness.

baldness (noun)	alopecia (noun)
the condition of having no hair on the top of the head	loss of hair (especially on the head) or loss of wool or feathers; in humans it can result from heredity or hormonal imbalance or certain diseases or drugs and treatments (chemotherapy for cancer)