Rocker

Rock·er

Rocker

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.
  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. Same as Rock shaft. (Mach.)

Phrases & Compounds
Rocker arm
an arm borne by a rock shaft.