eddy
A pocket of calm or reverse-flowing water behind an obstruction in a current — a boulder, a bridge piling, a river bend. The water circles back on itself, creating a small refuge in the middle of moving water. In whitewater paddling, catching an eddy is the fundamental survival skill — the ability to stop, rest, and read what's ahead.
Etymology
Old English ed- (back, again) + ēa (water). Related to Old Norse. The word has been in English for over a thousand years.
Notes
Already entered in the climbing batch — this is the expanded version with the paddling context. Use whichever feels right, or merge them.
*
Surprise Me With a Word