Some people might call it a leotard but the rowing world prefers to call it a one-piece as it's less embarrassing. Wear one when racing or training heavily and you want to make sure you have full bodily motion.

(of clothing) consisting of or fashioned in a single whole piece; "a one-piece garment"

An upgraded style of toilet which is configured of an integral tank and bowl which are formed as "one piece" during the manufacturing process. (Picture, scroll to "Vouge" model)