preen gland vs uropygial gland

preen gland and uropygial gland both are nouns.

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

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

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

preen gland (noun)	uropygial 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