baker's half dozen

Half of a "baker's dozen" (13 rather than 12), thus, 7 rather than 6. The term "baker's dozen" to mean 13 originates from an 11th-century practice in which bakers would include an extra loaf of bread in a dozen so as to avoid facing penalties for selling underweight bread. The seven deadly sins are a baker's half dozen of things one should avoid in order to live a moral life.