platonic year

GNU Webster's 1913

1. adj. (Astron.) a period of time determined by the revolution of the equinoxes, or the space of time in which the stars and constellations return to their former places in respect to the equinoxes; -- called also great year. This revolution, which is caused by the precession of the equinoxes, is accomplished in about 26,000 years.
2. n. See under Platonic, and Sabbatical.

WordNet 3.0

1. n. time required for one complete cycle of the precession of the equinoxes, about 25,800 years