shelduck vs sheldrake

shelduck and sheldrake both are nouns.

Word	Noun	Adjective	Verb	Adverb
shelduck	Yes	No	No	No
sheldrake	Yes	No	No	No

As nouns, sheldrake is a hypernym of shelduck; that is, sheldrake is a word with a broader meaning than shelduck:

shelduck: female sheldrake
sheldrake: Old World gooselike duck slightly larger than a mallard with variegated mostly black-and-white plumage and a red bill

shelduck (noun)	sheldrake (noun)
female sheldrake	Old World gooselike duck slightly larger than a mallard with variegated mostly black-and-white plumage and a red bill
	large crested fish-eating diving duck having a slender hooked bill with serrated edges