The Collaborative International Dictionary of English v.0.48:

Picket \Pick"et\, v. t. [imp. & p. p. Picketed; p. pr. & vb.
   n. Picketing.]
   1. To fortify with pointed stakes.
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   2. To inclose or fence with pickets or pales.
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   3. To tether to, or as to, a picket; as, to picket a horse.
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   4. To guard, as a camp or road, by an outlying picket.
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   5. To torture by compelling to stand with one foot on a
      pointed stake. [Obs.]
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