decade [LME] One book by the Roman historian Livy, who lived at the time of Christ, was in ten parts, and the name for each division was translated into English as decade. The earliest uses of the word in English refer to the sections of a similar literary work. It did not come to refer to a period of ten years until the early 17th century. The root of decade, Greek deka ‘ten’, is also that of *decimate and of the first element of units such as the decilitre and decimetre [L18th]. See also kilogram.