backwatern.[Back, a. or adv. + -water. ]1. Water turned back in its course by an obstruction, an opposing current, or the flow of the tide, as in a sewer or river channel, or across a river bar.()2. An accumulation of water overflowing the low lands, caused by an obstruction.()3. Water thrown back by the turning of a waterwheel, or by the paddle wheels of a steamer.()