Zastrugi \Zas*tru"gi\, n. pl.; sing. -ga. [Russ. zastruga furrow made on the shore by water.]

Grooves or furrows formed in snow by the action of the wind, and running parallel with the direction of the wind. This formation results from the erosion of transverse waves previously formed.

Source: Webster's Revised Unabridged Dictionary (1913)