purl

Unknown; apparently related to Scots and dialect pirl (“twist, ripple, whirl, spin”), and possibly to Older Scots pyrl ("thrust or poke at"). Compare Venetan pirlo, an embellishment where the woven threads are twisted together. May be unrelated to purfle, though the meanings are similar.

from Middle English pirle (“whirligig”), Middle Italian pirla (“whipping top”).

From Old Norse purla (“to babble”), possibly ultimately from an imitative Germanic base related to Dutch polder, Norwegian puldra (“to gush”) and pulla (“to bubble”), Old English polr (“marsh”).

Possibly from the pearl-like appearance caused by bubbles on the surface of the liquid.