Florida gallinule vs water hen

Florida gallinule and water hen both are nouns.

Word	Noun	Adjective	Verb	Adverb
Florida gallinule	Yes	No	No	No
water hen	Yes	No	No	No

As nouns, water hen is a hypernym of Florida gallinule; that is, water hen is a word with a broader meaning than Florida gallinule:

Florida gallinule: North American dark bluish-grey gallinule
water hen: any of various small aquatic birds of the genus Gallinula distinguished from rails by a frontal shield and a resemblance to domestic hens

Other hypernyms of Florida gallinule include gallinule, marsh hen, swamphen.

Florida gallinule (noun)	water hen (noun)
North American dark bluish-grey gallinule	any of various small aquatic birds of the genus Gallinula distinguished from rails by a frontal shield and a resemblance to domestic hens
	a coot found in North America