Diamond Head is the name of a volcanic tuff cone on the Hawaiian island of O'ahu and known to Hawaiians as Le'ahi, most likely from lae 'browridge, promontory' plus ahi 'tuna' because the shape of the ridgeline resembles the shape of a tuna's dorsal fin. Its English name was given by British sailors in the 19th century, who mistook calcite crystals embedded in the rock for diamonds.