to be at loggerheads

from 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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