hypothyroidism vs gland disease

hypothyroidism and gland disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
hypothyroidism	Yes	No	No	No
gland disease	Yes	No	No	No

As nouns, gland disease is a hypernym of hypothyroidism; that is, gland disease is a word with a broader meaning than hypothyroidism:

hypothyroidism: an underactive thyroid gland; a glandular disorder resulting from insufficient production of thyroid hormones
gland disease: a disorder of the glands of the body

Other hypernyms of hypothyroidism include adenosis, glandular disease, glandular disorder.

hypothyroidism (noun)	gland disease (noun)
an underactive thyroid gland; a glandular disorder resulting from insufficient production of thyroid hormones	a disorder of the glands of the body