actually I decided to double check this and all three of “beachball”, “beach-ball”, and beach ball are used, but “beach ball” is by far the most popular starting from around the late 1920’s, even when supposedly the first beach ball was invented in 1938 (I’ll leave figuring out the beach ball conspiracy for later). From there, “beachball” and “beach-ball” were mostly equally used until the late 1950’s where “beachball” took over. Also, beach balls have been on a decline since 2012, so I don’t blame you for forgetting that it was a word. “Beachball” has also been on a decline while “beach-ball” stays strong, so don’t abandon your spelling just yet, it might take second soon.