uropygial gland vs preen gland

uropygial gland and preen gland both are nouns.

Word	Noun	Adjective	Verb	Adverb
uropygial gland	Yes	No	No	No
preen gland	Yes	No	No	No

As nouns, uropygial gland and preen gland are synonyms defined as:

uropygial gland and preen gland: oil-secreting gland situated at the base of the tail in most birds

uropygial gland (noun)	preen gland (noun)
oil-secreting gland situated at the base of the tail in most birds	oil-secreting gland situated at the base of the tail in most birds