Etymology Possible alteration of ruffle, from Middle English ruffelen, akin to Low German ruffelen (“to crumple”).
1
A swift, shallow part of a stream causing broken water.
They then proceeded below the milldam, where there was a strong riffle, with likely looking pools and eddies1903, James Alexander Henshall, Bass, Pike, Perch and other Game Fishes of America:
The big trout feed aggressively and tend to lose their caution in the rifles.2017, Bill Barich, “On the Glories of Autumn”, in California Fly Fisher:
1 more example
[...] Brook Drain has now been diverted into a newly dug replacement river section [...]. It has been designed in conjunction with the Environment Agency to hold a much larger volume of water, in order to help with local flooding issues. It also features riffles (shallow sections of water) and side pools where aquatic wildlife can take shelter during storms.2020 April 8, Paul Stephen, “ECML dive-under drives divergence”, in Rail, page 43:
2
A succession of small waves.
3
Business, Mining 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 trough.
To shuffle playing cards by separating the deck in two and sliding the thumbs along the edges of the cards to mix the two parts.
6
To idly manipulate objects with the fingers.
7
To prepare samples of material using a riffler.
riffle
noun
Etymology From Danish [Term?] (“a groove”). Compare rifle (“to score, to make grooves”) and the past participle riflet (“scored, grooved, rifled”), riffeln with the same meaning. Also see rifle (“a rifled gun”).
1
In seal engraving, a small metal disc at the end of a tool.