The Collaborative International Dictionary of English v.0.48:

Loggerhead \Log"ger*head`\, n. [Log + head.]
   1. A blockhead; a dunce; a numskull. --Shak. Milton.
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   2. A spherical mass of iron, with a long handle, used to heat
      tar.
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   3. (Naut.) An upright piece of round timber, in a whaleboat,
      over which a turn of the line is taken when it is running
      out too fast. --Ham. Nav. Encyc.
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   4. (Zool.) A very large marine turtle (Thalassochelys
      caretta syn. Thalassochelys caouana), common in the
      warmer parts of the Atlantic Ocean, from Brazil to Cape
      Cod; -- called also logger-headed turtle.
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   5. (Zool.) An American shrike (Lanius Ludovicianus),
      similar to the butcher bird, but smaller. See Shrike.
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   To be at loggerheads, To fall to loggerheads, or To go
   to loggerheads, to quarrel; to be at strife. --L' Estrange.
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