a. (Naut.) Having sides inclining inwards, as a ship; -- opposed to
n. [ Back, a. + side. ] The hinder part, posteriors, or rump of a person or animal. [ 1913 Webster ]
☞ Backside (one word) was formerly used of the rear part or side of any thing or place, but in such senses is now two words. [ 1913 Webster ]