bird vs air sac

bird and air sac both are nouns.

Word	Noun	Adjective	Verb	Adverb
bird	Yes	No	Yes	No
air sac	Yes	No	No	No

bird (noun)	air sac (noun)
warm-blooded egg-laying vertebrates characterized by feathers and forelimbs modified as wings	any of the membranous air-filled extensions of the lungs of birds
badminton equipment consisting of a ball of cork or rubber with a crown of feathers	any of the thin-walled extensions of the tracheae of insects
a cry or noise made to express displeasure or contempt	a tiny sac for holding air in the lungs; formed by the terminal dilation of tiny air passageways
the flesh of a bird or fowl (wild or domestic) used as food
informal terms for a (young) woman

bird (verb)	air sac (verb)
watch and study birds in their natural habitat