The Collaborative International Dictionary of English v.0.48:

Stopper \Stop"per\, n.
   1. One who stops, closes, shuts, or hinders; that which stops
      or obstructs; that which closes or fills a vent or hole in
      a vessel.
      [1913 Webster]

   2. (Naut.) A short piece of rope having a knot at one or both
      ends, with a lanyard under the knot, -- used to secure
      something. --Totten.
      [1913 Webster]

   3. (Bot.) A name to several trees of the genus Eugenia, found
      in Florida and the West Indies; as, the red stopper. See
      Eugenia. --C. S. Sargent.
      [1913 Webster]

   Ring stopper (Naut.), a short rope or chain passing through
      the anchor ring, to secure the anchor to the cathead.

   Stopper bolt (Naut.), a large ringbolt in a ship's deck, to
      which the deck stoppers are hooked.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Stopper \Stop"per\, v. t. [imp. & p. p. Stoppered; p. pr. &
   vb. n. Stoppering.]
   To close or secure with a stopper.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stopper
    n 1: an act so striking or impressive that the show must be
         delayed until the audience quiets down [syn: show-
         stopper, showstopper, stopper]
    2: a remark to which there is no polite conversational reply
       [syn: conversation stopper, stopper]
    3: (bridge) a playing card with a value sufficiently high to
       insure taking a trick in a particular suit; "if my partner
       has a spade stopper I can bid no trump"
    4: blockage consisting of an object designed to fill a hole
       tightly [syn: plug, stopper, stopple]
    v 1: close or secure with or as if with a stopper; "She
         stoppered the wine bottle"; "The mothers stoppered their
         babies' mouths with pacifiers" [syn: stopper, stopple]