n. 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. at loggerheads (often foll. by with) disagreeing or disputing.
[ prob. f. dial. logger block of wood for hobbling a horse + HEAD ]