Definition of: loggerhead

(lôg′ər·hed′, log′-) noun
1. A blockhead; dunce.
2. A large marine turtle (genus Caretta) of tropical Atlantic waters.
3. The loggerhead shrike. See under SHRIKE.
4. A post on the gunwale of a whaleboat around which the line is turned to retard the motion of a harpooned whale.
—at loggerheads Engaged in a quarrel; unable to agree. [<dial. E logger log tied to a horse's leg to impede movement + HEAD]