Fœtus or foetus is the British, Irish and Commonwealth spelling, which has been in use since at least 1594. It arose as a hypercorrection based on an incorrect etymology (i.e. due to insufficient knowledge of Latin) that may have originated with an error by Saint Isidore of Seville, in AD 620. This spelling is the most common in most English-speaking countries (except in medical literature). The original spelling based on the Latin etymology fetus however persists in Canada and the United States. In addition, fetus is now also the standard English spelling throughout the world in medical journals. The spelling ""faetus"" was used historically.