moorhen vs gallinule

moorhen and gallinule both are nouns.

Word	Noun	Adjective	Verb	Adverb
moorhen	Yes	No	No	No
gallinule	Yes	No	No	No

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

moorhen: black gallinule that inhabits ponds and lakes
gallinule: 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 moorhen include marsh hen, swamphen, water hen.

moorhen (noun)	gallinule (noun)
black gallinule that inhabits ponds and lakes	any of various small aquatic birds of the genus Gallinula distinguished from rails by a frontal shield and a resemblance to domestic hens
female red grouse