Ở đây theo ḿnh nghĩ có sự lấn cấn giữa đông và tây .
Một kỷ theo tự điển Hán Việt là 12 năm ,đó là kỷ của nhiều nước phương đông .
Một kỷ là từ dịch từ chữ
decade th́ chỉ có 10 năm .Thế kỷ ,thiên niên kỷ...cũng do cách dịch này mà ra .
(A decade is a period of 10 years. The word is derived (via French and Latin) from the Ancient Greek dekas which means ten. Other words for spans of years also come from Latin: biennium, triennium, quadrennium (4 years), lustrum (5 years), century (100 years), millennium (1000 years).
Although any period of 10 years is a decade,[1][2] a convenient and frequently referenced interval is based on the tens digit of a calendar year, as in using "1960s" to represent the decade from 1960 to 1969.[3][4] Often, for brevity, only the tens part is mentioned (60s or sixties), although this may leave it uncertain which century is meant. These references are frequently used to encapsulate popular culture or other widespread phenomena that dominated such a decade, as in The Great Depression of the 1930s.
Because the common calendar starts with year 1, its first full decade is the years 1 to 10, the second decade from 11 to 20, and so on.[5] So although the "1960s" comprises the years 1960 to 1969, the "197th decade" spans 1961 to 1970. )
Nguồn
https://en.wikipedia.org/wiki/Decade