Back"wa`ter (?), n. [Back, a. or adv. + -ward. ]
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.
An accumulation of water overflowing the low lands, caused by an obstruction.
Water thrown back by the turning of a waterwheel, or by the paddle wheels of a steamer.
© Webster 1913.