"knit with inverted stitches," 1825; earlier "embroider with gold or silver thread" (1520s), probably from Middle English pirlyng "revolving, twisting," of unknown origin. The two senses usually are taken as one word, but even this is not certain. Klein suggests a source in Italian pirolare "to twirl," from pirolo "top." As a noun, from late 14c. as "bordering, frills," 1530s as "twisted thread of gold and silver."
"flow with a murmuring sound," 1580s, imitative, perhaps from a Scandinavian language. Related: Purled; purling.