A decade (pronounce: DEK-aid) is a period of 10 years. The word comes from the Ancient Greek word for ten: "deka". 10 decades make a century, while 100 decades make a millennium. Formally, a decade is a period starting with a year of which the last digit is 1 and ending the following year which is a multiple of ten: For example, the period from 2001 to 2010 was the 1st decade of the 21st century (or the 201st decade). Although, the most common way to count decades is counting from the representing digit, like the nineteen-eighties (1980s) referring to the period from 1980 to 1989 and the nineteen-nineties (1990s) referring to the period from 1990 to 1999. However, these two periods are formally no decades as the last year of these periods, 1989 and 1999, are not multiples of ten.