What Do You Mean by the Term by the Skin of Your Teeth?
If you pass a test by just a few points or win a contest by a tiny bit, people might say you did so “by the skin of your teeth.” In other words, you just barely did it. The only problem with this expression is that your teeth don’t have skin! But sometimes they have a film on them, especially first thing in the morning. If you feel that sticky film, it’s time to brush your teeth!
The phrase first appears in English in the Geneva Bible, 1560, in Job 19:20, which provides a literal translation of the original Hebrew: “I haue escaped with the skinne of my tethe.”
Teeth don’t have skin, of course, so the writer may have been alluding to the teeth’s surface or simply to a notional minute measure – something that might now be referred to, with less poetic imagery than the biblical version, as ‘as small as the hairs on a gnat’s bollock’.