The Collaborative International Dictionary of English v.0.48:

Winterkill \Win"ter*kill`\, v. t. [imp. & p. p. Winterkilled;
   p. pr. & vb. n. Winterkilling.]
   To kill by the cold, or exposure to the inclemency of winter;
   as, the wheat was winterkilled. [U. S.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Winterkill \Win"ter*kill`\, v. i.
   To die as the result of exposure to the cold of winter; as,
   the tree winterkills easily.
   [Webster 1913 Suppl.]