oystercatcher vs oyster catcher

oystercatcher and oyster catcher both are nouns.

Word	Noun	Adjective	Verb	Adverb
oystercatcher	Yes	No	No	No
oyster catcher	Yes	No	No	No

As nouns, oystercatcher and oyster catcher are synonyms defined as:

oystercatcher and oyster catcher: black-and-white shorebird with stout legs and bill; feed on oysters etc.

oystercatcher (noun)	oyster catcher (noun)
black-and-white shorebird with stout legs and bill; feed on oysters etc.	black-and-white shorebird with stout legs and bill; feed on oysters etc.