riffle

Etymology 1

Possible alteration of ruffle, from Middle English ruffelen, akin to Low German ruffelen (“to crumple”).

noun

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 eddies 1903, 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
   … 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. April 8 2020, Paul Stephen, “ECML dive-under drives divergence”, in Rail, page 43
2. A succession of small waves.
3. (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.
4. A quick skim through the pages of a book.
5. The act of shuffling cards; the sound made while shuffling cards.

verb

1. (intransitive) To flow over a swift, shallow part of a stream.
2. (transitive) To ruffle with a rippling action.
3. (intransitive) To skim or flick through the pages of a book.
4. (transitive) To leaf through rapidly.
5. (transitive) 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. (transitive) To idly manipulate objects with the fingers.
7. (transitive) To prepare samples of material using a riffler.

Etymology 2

Danish [Term?] (“a groove”)

noun

1. In seal engraving, a small metal disc at the end of a tool.