horsehead vs horse-head

horsehead and horse-head both are nouns.

Word	Noun	Adjective	Verb	Adverb
horsehead	Yes	No	No	No
horse-head	Yes	No	No	No

As nouns, horsehead and horse-head are synonyms defined as:

horsehead and horse-head: any of several silvery marine fishes with very flat bodies

Other synonyms of horsehead include Atlantic moonfish, dollarfish, horsefish, moonfish, Selene setapinnis.

horsehead (noun)	horse-head (noun)
any of several silvery marine fishes with very flat bodies	any of several silvery marine fishes with very flat bodies