add. ·noun a ripple in a stream or current of water; also, a place where the water ripples, as on a shallow rapid.
2. riffle ·noun a trough or sluice having cleats, grooves, or steps across the bottom for holding quicksilver and catching particles of gold when auriferous earth is washed; also, one of the cleats, grooves, or steps in such a trough. also called ripple.