thymus vs ductless gland

thymus and ductless gland both are nouns.

Word	Noun	Adjective	Verb	Adverb
thymus	Yes	No	No	No
ductless gland	Yes	No	No	No

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

thymus: a ductless glandular organ at the base of the neck that produces lymphocytes and aids in producing immunity; atrophies with age
ductless gland: any of the glands of the endocrine system that secrete hormones directly into the bloodstream

Other hypernyms of thymus include endocrine, endocrine gland.

thymus (noun)	ductless gland (noun)
a ductless glandular organ at the base of the neck that produces lymphocytes and aids in producing immunity; atrophies with age	any of the glands of the endocrine system that secrete hormones directly into the bloodstream