duck-billed vs duckbill

duck-billed is not a noun while duckbill is a noun.

Word	Noun	Adjective	Verb	Adverb
duck-billed	No	Yes	No	No
duckbill	Yes	Yes	No	No

As adjectives, duck-billed and duckbill are synonyms defined as:

duck-billed (noun)	duckbill (noun)
	small densely furred aquatic monotreme of Australia and Tasmania having a broad bill and tail and webbed feet; only species in the family Ornithorhynchidae
	primitive fish of the Mississippi valley having a long paddle-shaped snout

duck-billed (adjective)	duckbill (adjective)
having a beak resembling that of a duck	having a beak resembling that of a duck