The Collaborative International Dictionary of English v.0.48:

Harrow \Har"row\ (h[a^]r"r[-o]), n. [OE. harowe, harwe, AS.
   hearge; cf. D. hark rake, G. harke, Icel. herfi harrow, Dan.
   harve, Sw. harf. [root]16.]
   1. An implement of agriculture, usually formed of pieces of
      timber or metal crossing each other, and set with iron or
      wooden teeth. It is drawn over plowed land to level it and
      break the clods, to stir the soil and make it fine, or to
      cover seed when sown.
      [1913 Webster]

   2. (Mil.) An obstacle formed by turning an ordinary harrow
      upside down, the frame being buried.
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   Bush harrow, a kind of light harrow made of bushes, for
      harrowing grass lands and covering seeds, or to finish the
      work of a toothed harrow.

   Drill harrow. See under 6th Drill.

   Under the harrow, subjected to actual torture with a
      toothed instrument, or to great affliction or oppression.
      [1913 Webster]