osier n.

species of willow with tough, flexible branches used in basket-work, c. 1300, "a willow switch," from 14c. of the tree itself, from Old French osier, ozier "willow twig" (13c.) and directly from Medieval Latin osera, osiera "willow," ausaria "willow bed," a word of unknown origin, perhaps from Gaulish. Old English had the word as oser, from Medieval Latin.