overshoe

from WordNet (r) 3.0 (2006)

overshoe
    n 1: footwear that protects your shoes from water or snow or
         cold

from The Collaborative International Dictionary of English v.0.48

Overshoe \O"ver*shoe`\, n.
   A shoe that is worn over another for protection from wet or
   for extra warmth; esp., an India-rubber shoe; a galosh.
   [1913 Webster]