loggerhead

n. [ Log + head. ] 1. A blockhead; a dunce; a numskull. Shak. Milton. [ 1913 Webster ]

2. A spherical mass of iron, with a long handle, used to heat tar. [ 1913 Webster ]

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. [ 1913 Webster ]

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. [ 1913 Webster ]

5. (Zool.) An American shrike (Lanius Ludovicianus), similar to the butcher bird, but smaller. See Shrike. [ 1913 Webster ]

To be at loggerheads,
To fall to loggerheads, or
To go to loggerheads, to quarrel; to be at strife. L' Estrange. [ 1913 Webster ]