Wind sprites are one type of sprite; creatures which are described in the ancient "Booke" which has been memorized by the village eldress in Lower Posada. They are usually considered to be friendly air spirits, but possibly they also have a mischievous streak. In Polish there are several equivalent terms: "płanetnik", "chmurnik" or "obłocznik".
"Cloud sprites and wind sprites be varied. Some rain pour, some wind roar, others hurl their thunder. Harvests to protect from them, takest thou a knife of iron, new, of a mouse's droppings a half ounce, of a grey heron's fat—" - pg.179, The Last Wish (UK edition)
"...The easiest access they find at cottages of honest, simple, and unwitting peasants who readily ascribe all misfortune and ill events to spells, unnatural creatures and monsters, the doings of windsprites or evil spirits. Instead of praying to the gods, instead of bearing rich offerings to the temple, such a simpleton is ready to give his last penny to the base witcher, believing the witcher, the godless changeling, will turn around his fate and save him from misfortune." - pg.165, Blood of Elves (UK edition)