moorhen vs swamphen

moorhen and swamphen both are nouns.

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

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

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

moorhen (noun)	swamphen (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