Source : Webster's Revised Unabridged Dictionary (1913)

Rocker \Rock"er\, n.
   1. One who rocks; specifically, one who rocks a cradle.

            It was I, sir, said the rocker, who had the honor,
            some thirty years since, to attend on your highness
            in your infancy.                      --Fuller.

   2. One of the curving pieces of wood or metal on which a
      cradle, chair, etc., rocks.

   3. Any implement or machine working with a rocking motion, as
      a trough mounted on rockers for separating gold dust from
      gravel, etc., by agitation in water.

   4. A play horse on rockers; a rocking-horse.

   5. A chair mounted on rockers; a rocking-chair.

   6. A skate with a curved blade, somewhat resembling in shape
      the rocker of a cradle.

   7. (Mach.) Same as {Rock shaft}.

   {Rocker arm} (Mach.), an arm borne by a rock shaft.

Source : WordNet®

rocker
     n 1: an attendant who rocks a child in a cradle
     2: a performer or composer or fan of rock music [syn: {rock 'n'
        roll musician}]
     3: a teenager or young adult in the 1960s who wore leather
        jackets and rode motorcycles
     4: a chair mounted on rockers [syn: {rocking chair}]
     5: a trough on rockers used by gold miners to shake earth in
        water in order to separate the gold [syn: {cradle}]
     6: an ice skate with a curved blade
     7: a curved support that permits the supported object to rock
        to and fro