The word bissextile in fact has its origins in the sixteenth century, deriving from the Latin term bissextilis meaning ‘having an intercalary day’. In the ancient Roman calendar, the sixth day before the ‘Calends of March’ (i.e. 24th February, counting back from the beginning of March) occurred twice in a leap year. Hence the term is based on Latin sextus – ‘six’ – and bis – ‘twice’ – and means ‘twice the sixth day’. The word bissextile is relatively rare in modern English, but emerges from obscurity every four years as illustrated by articles like the one cited above. The phrase année bissextile is however a commonly used French term for leap year.