The Collaborative International Dictionary of English v.0.48:
Purl \Purl\, v. i. [imp. & p. p. Purled; p. pr. & vb. n.
Purling.] [Cf. Sw. porla, and E. pur to murmur as a cat.]
1. To run swiftly round, as a small stream flowing among
stones or other obstructions; to eddy; also, to make a
murmuring sound, as water does in running over or through
Swift o'er the rolling pebbles, down the hills,
Louder and louder purl the falling rills. --Pope.
2. [Perh. fr. F. perler to pearl, to bead. See Pearl, v. &
n.] To rise in circles, ripples, or undulations; to curl;
thin winding breath which purled up to the sky.