The Collaborative International Dictionary of English v.0.48:

Whisker \Whisk"er\, n.
   [1913 Webster]
   1. One who, or that which, whisks, or moves with a quick,
      sweeping motion.
      [1913 Webster]

   2. Formerly, the hair of the upper lip; a mustache; --
      usually in the plural.
      [1913 Webster]

            Hoary whiskers and a forky beard.     --Pope.
      [1913 Webster]

   3. pl. That part of the beard which grows upon the sides of
      the face, or upon the chin, or upon both; as, side
      whiskers; chin whiskers.
      [1913 Webster]

   4. A hair of the beard.
      [1913 Webster]

   5. One of the long, projecting hairs growing at the sides of
      the mouth of a cat, or other animal.
      [1913 Webster]

   6. pl. (Naut.) Iron rods extending on either side of the
      bowsprit, to spread, or guy out, the stays, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

whisker
    n 1: a very small distance or space; "they escaped by a
         hair's-breadth"; "they lost the election by a whisker"
         [syn: hair's-breadth, hairsbreadth, hair, whisker]
    2: a long stiff hair growing from the snout or brow of most
       mammals as e.g. a cat [syn: whisker, vibrissa, sensory
       hair]
    v 1: furnish with whiskers; "a whiskered jersey" [syn:
         bewhisker, whisker]