(n.) the pool of water beneath a waterwheel
Essential waterwheel knowledge: the boards around a waterwheel are called awes, and the pool of water the wheel tips into is called the pulrose.
(You can add to that the fact that the inner wheel of a waterwheel is called the sole, and if the wheel is fitted with buckets rather than paddles then they’re properly called scoops.)
The word pulrose is an interesting one. As quintessentially English as it appears, its more usual spelling is polroz, and in that guise it’s more specifically used in reference to the pools of water beneath the wheels used in tin mines. As that definition might suggest, polroz is a Cornish word, and derives from the Cornish words pol (meaning ‘pool’) and ros, or roz (meaning ‘wheel’). Although Cornish is a Celtic language, there’s some obvious etymological parallels here between pol and pool, and even roz is a distant relative of words like rota, rotor and rotation.
So pulrose is really nothing more than an anglicised version of polroz. Though it’ll win you a few less points in Scrabble.