The Collaborative International Dictionary of English v.0.48:

Rock \Rock\, v. t. [imp. & p. p. Rocked;p. pr. & vb. n.
   Rocking.] [AS. roccian; akin to Dan. rokke to move, to
   snake; cf. Icel. rukkja to pull, move, G. r["u]cken to move,
   push, pull.]
   1. To cause to sway backward and forward, as a body resting
      on a support beneath; as, to rock a cradle or chair; to
      cause to vibrate; to cause to reel or totter.
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            A rising earthquake rocked the ground. --Dryden.
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   2. To move as in a cradle; hence, to put to sleep by rocking;
      to still; to quiet. "Sleep rock thy brain." --Shak.
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   Note: Rock differs from shake, as denoting a slower, less
         violent, and more uniform motion, or larger movements.
         It differs from swing, which expresses a vibratory
         motion of something suspended.
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