Year "year", originally 秂, an ideographic compound of a person carrying a bundle of wheat denoting "harvest". Slavic besides "godŭ" "time period; year" uses "lěto" "summer; year". In the International System of Quantities (ISO 80000-3), the year (symbol, "a") is defined as either 365 days or 366 days. No astronomical year has an integer number of days or lunar months, so any calendar that follows an astronomical year must have a system of intercalation such as leap years. In the Julian calendar, the average (mean) length of a year is 365.25 days. In a non-leap year, there are 365 days, in
Leap year In 1825, Ideler believed that the lunisolar calendar was abandoned about 450 BC by the decemvirs, who implemented the Roman Republican calendar, used until 46 BC. The days of these calendars were counted down (inclusively) to the next named day, so February 24 was "ante diem sextum Kalendas Martias" ("the sixth day before the calends of March") often abbreviated a. d. VI Kal. Mart. The Romans counted days inclusively in their calendars, so this was actually the fifth day before March 1 when counted in the modern exclusive manner (not including the starting day). The Republican calendar's intercalary month was