tooth [OE] An Old English word from an ancient root shared by Latin dens, the source of dental [L16th], dentist [M18th], trident [L16th] ‘three teeth’, and *indent. To fight tooth and nail was in the 16th century to fight with tooth and nail. Although in a real fight this would mean ‘by biting and scratching’, the phrase is almost always used of non-physical struggles. To set someone’s teeth on edge [LME] comes from the Bible, and expresses the unpleasant sensation felt when you have bitten into something that is bitter or sour: ‘Every man that hath eaten the sour grape, his teeth shall be set on edge’ (Jeremiah). See also hen.