at loggerheads Definition

loggerhead
noun

1. A large sea turtle with a big head, whose shell can be up to 0.9m (3ft) long and which weighs around 136kg (300lb).

Form: loggerhead turtle (also)
2. A device with a long handle and a metal sphere at the end, which is heated and plunged into liquids such as tar to melt them.

Idiom: at loggerheads

Arguing or disagreeing fiercely

Etymology: apparently from the use of the tar-melter as a weapon. &clock; 16c as logger a dialect word meaning ‘something heavy and clumsy' + head.