1.
cold autumn/winter wind that blows the leaves off trees
a cold, dry wind that signals the arrival of winter, typically blowing from late autumn to early winter
Etymology
Literally "tree-witherer": 木 (tree, an old reading) + 枯らす (to wither), the cold, dry wind of late autumn and early winter that strips trees bare.
Cultural note
木枯らし一号, the first such north wind of the season, is announced by the Japan Meteorological Agency for the Tokyo and Osaka regions, usually between late October and November, as a sign that winter is near. In poetry it is a winter season word.