The Collaborative International Dictionary of English v.0.48:

Winter's bark \Win"ter's bark`\ (Bot.)
   The aromatic bark of tree (Drimys Winteri syn. Drymis
   Winteri) of the Magnolia family, which is found in Southern
   Chile. It was first used as a cure for scurvy by its
   discoverer, Captain John Winter, vice admiral to sir Francis
   Drake, in 1577.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Drimys winteri
    n 1: South American evergreen tree yielding winter's bark and a
         light soft wood similar to basswood [syn: winter's bark,
         winter's bark tree, Drimys winteri]