means To narrow something down by separating the valuable parts from the worthless ones, removing what you don't want until only the good remains.

from From Old English 'windwian,' to fan or expose to the wind — and yes, that's the same 'wind' that blows. The word is rooted in the literal farm task of tossing threshed grain into the breeze so the light, useless chaff drifts away while the heavier kernels fall back to the ground. The breeze did the sorting; the farmer just kept throwing. Over time the airborne sifting became a metaphor for any careful sorting, but the wind is still right there in the spelling.