From Middle High German riffeln, rifilen, from Old High German riffilōn (“to ripple, remove seeds from flax”), derived from riffila (“ripple”), from Proto-Germanic *ripilō, which is probably related to *rīpaną (“to harvest, reap”). Cognate with Dutch repel, English ripple.
The sense “to cut grooves into” is from unrelated German Low German rieveln, riffeln, frequentative of Middle Low German rīven (“to rake”). Compare German Riefe (“groove”), Dutch rijf (“rake”), (obsolete) rijffelen (“to scrape”), Old Norse hrīfa (“rake”). These words are all rather related to Proto-Germanic *hrībaną (“to rake, scratch”).
riffeln (weak, third-person singular present riffelt, past tense riffelte, past participle geriffelt, auxiliary haben)
| infinitive | riffeln | ||||
|---|---|---|---|---|---|
| present participle | riffelnd | ||||
| past participle | geriffelt | ||||
| auxiliary | haben | ||||
| indicative | subjunctive | ||||
| singular | plural | singular | plural | ||
| present | ich riffle ich riffele ich riffel |
wir riffeln | i | ich riffele ich riffle |
wir riffeln |
| du riffelst | ihr riffelt | du riffelest du rifflest |
ihr riffelet ihr rifflet | ||
| er riffelt | sie riffeln | er riffele er riffle |
sie riffeln | ||
| preterite | ich riffelte | wir riffelten | ii | ich riffelte1 | wir riffelten1 |
| du riffeltest | ihr riffeltet | du riffeltest1 | ihr riffeltet1 | ||
| er riffelte | sie riffelten | er riffelte1 | sie riffelten1 | ||
| imperative | riffle (du) riffel (du) riffele (du) |
riffelt (ihr) | |||
1Rare except in very formal contexts; alternative in würde normally preferred.