dart board vs dartboard

dart board and dartboard both are nouns.

Word	Noun	Adjective	Verb	Adverb
dart board	Yes	No	No	No
dartboard	Yes	No	No	No

As nouns, dart board and dartboard are synonyms defined as:

dart board and dartboard: a circular board of wood or cork used as the target in the game of darts

dart board (noun)	dartboard (noun)
a circular board of wood or cork used as the target in the game of darts	a circular board of wood or cork used as the target in the game of darts