The Collaborative International Dictionary of English v.0.48:

moleskin \mole"skin`\ (m[=o]l"sk[i^]n), n.
   1. Any fabric having a thick soft shag, like the fur of a
      mole; esp., a kind of strong twilled fustian.
      [1913 Webster]

   2. A soft fabric having an adhesive backing, applied to the
      skin at points susceptible to abrasion, as on the feet, to
      prevent irritation or blistering during exercise, such as
      hiking.
      [PJC]

WordNet (r) 3.0 (2006):

moleskin
    n 1: a durable cotton fabric with a velvety nap