loggerheads [L16th] The origins of at loggerheads are obscure. The earliest meanings of loggerhead, dating from the late 16th century, were ‘a disproportionately large head’ and ‘a stupid person’ (similar to mid 16th-century blockhead). Around half a century later the word was applied to various animals with very large heads, notably the loggerhead turtle. In the 1670s it started to be used in the plural for people disagreeing, but the reason for this is obscure.