Emily Dickinson Lexicon

PURL, v.i. [Sw. porla; W. freulaw, to purl, to ripple; fraul, a rippling. It may be allied to G. brüllen, D. brullen, Dan. broler, to roar, and to Eng. frill, trill and roll.]

1. To murmur, as a small stream flowing among stones or other obstructions, which occasion a continued series of broken sounds. It is applied only to small streams. Large streams running in like manner are said to roar. In descriptions of rural scenery, the poets seldom omit a purling brook or stream. My flowery theme, / A painted mistress or a purling stream. – Pope.
2. To flow or run with a murmuring sound. Around th' adjoining brook that purls along / The vocal grove, now fretting o'er a rock. – Thomson.