1 an iron instrument with a ball at the end heated for melting pitch etc.
2 any of various large-headed animals, esp. a turtle (Caretta caretta) or shrike (Lanius ludovicianus).
3 archaic a blockhead or fool.
Phrases and idioms:
at loggerheads (often foll. by with) disagreeing or disputing.
Etymology: prob. f. dial. logger block of wood for hobbling a horse + HEAD
Useful english dictionary. 2012.