The Collaborative International Dictionary of English v.0.48:

Sucker \Suck"er\ (s[u^]k"[~e]r), n.
   1. One who, or that which, sucks; esp., one of the organs by
      which certain animals, as the octopus and remora, adhere
      to other bodies.
      [1913 Webster]

   2. A suckling; a sucking animal. --Beau. & Fl.
      [1913 Webster]

   3. The embolus, or bucket, of a pump; also, the valve of a
      pump basket. --Boyle.
      [1913 Webster]

   4. A pipe through which anything is drawn.
      [1913 Webster]

   5. A small piece of leather, usually round, having a string
      attached to the center, which, when saturated with water
      and pressed upon a stone or other body having a smooth
      surface, adheres, by reason of the atmospheric pressure,
      with such force as to enable a considerable weight to be
      thus lifted by the string; -- used by children as a
      plaything.
      [1913 Webster]

   6. (Bot.) A shoot from the roots or lower part of the stem of
      a plant; -- so called, perhaps, from diverting nourishment
      from the body of the plant.
      [1913 Webster]

   7. (Zool.)
      (a) Any one of numerous species of North American
          fresh-water cyprinoid fishes of the family
          Catostomidae; so called because the lips are
          protrusile. The flesh is coarse, and they are of
          little value as food. The most common species of the
          Eastern United States are the northern sucker
          (Catostomus Commersoni), the white sucker
          (Catostomus teres), the hog sucker (Catostomus
          nigricans), and the chub, or sweet sucker (Erimyzon
          sucetta). Some of the large Western species are
          called buffalo fish, red horse, black horse, and
          suckerel.
      (b) The remora.
      (c) The lumpfish.
      (d) The hagfish, or myxine.
      (e) A California food fish (Menticirrus undulatus)
          closely allied to the kingfish
      (a); -- called also bagre.
          [1913 Webster]

   8. A parasite; a sponger. See def. 6, above.
      [1913 Webster]

            They who constantly converse with men far above
            their estates shall reap shame and loss thereby; if
            thou payest nothing, they will count thee a sucker,
            no branch.                            --Fuller.
      [1913 Webster]

   9. A hard drinker; a soaker. [Slang]
      [1913 Webster]

   10. A greenhorn; someone easily cheated, gulled, or deceived.
       [Slang, U.S.]
       [1913 Webster]

   11. A nickname applied to a native of Illinois. [U. S.]
       [1913 Webster]

   12. A person strongly attracted to something; -- usually used
       with for; as, he's a sucker for tall blondes.
       [PJC]

   11. Any thing or person; -- usually implying annoyance or
       dislike; as, I went to change the blade and cut my finger
       on the sucker. [Slang]
       [PJC]

   Carp sucker, Cherry sucker, etc. See under Carp,
      Cherry, etc.

   Sucker fish. See Sucking fish, under Sucking.

   Sucker rod, a pump rod. See under Pump.

   Sucker tube (Zool.), one of the external ambulacral tubes
      of an echinoderm, -- usually terminated by a sucker and
      used for locomotion. Called also sucker foot. See
      Spatangoid.
      [1913 Webster]