The Collaborative International Dictionary of English v.0.48:

gumshoe \gum"shoe\ n.
   1. A detective; a private eye. [slang]
      [PJC]

   2. A shoe made of rubber, as a rubber overshoe.
      [PJC]

   3. A sneaker[3].
      [PJC]

WordNet (r) 3.0 (2006):

gumshoe
    n 1: someone who is a detective [syn: dick, gumshoe,
         hawkshaw]
    2: a waterproof overshoe that protects shoes from water or snow
       [syn: arctic, galosh, golosh, rubber, gumshoe]