Platonic year

noun Astronomy.

a period of about 26,000 years, equal to the time required for a complete revolution of the equinoxes.

Compare precession of the equinoxes.

Origin of Platonic year

First recorded in 1630–40

Also called great year.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018