paddle-box vs paddle box

paddle-box and paddle box both are nouns.

Word	Noun	Adjective	Verb	Adverb
paddle-box	Yes	No	No	No
paddle box	Yes	No	No	No

As nouns, paddle-box and paddle box are synonyms defined as:

paddle-box and paddle box: a wooden covering for the upper part of a paddlewheel

paddle-box (noun)	paddle box (noun)
a wooden covering for the upper part of a paddlewheel	a wooden covering for the upper part of a paddlewheel