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