Yén

Yén (plural yéni) is Quenya for "long year" or "great year", and was a unit of time used by the Elves of Middle-earth after the first rising of the Sun. Compare with a Valian Year, the unit of time used in Valinor.

1 yén = 144 solar years = 52,596 days

Tolkien used Valian Years to measure the passing of time in the Elder Days as recorded in the Annals of Aman, but such a Valian Years equals 9.582 solar years = 3500 days (in older versions, the Annals of Valinor, it equals 10 solar years).