1911 Encyclopædia Britannica/Trepidation

TREPIDATION (from Lat. trepidare, to tremble), a term meaning, in general, fear or trembling, but used technically in astronomy for an imagined slow oscillation of the ecliptic, having a period of 7000 years, introduced by the Arabian astronomers to explain a supposed variation in the precession of the equinoxes. It figured in astronomical tables until the time of Copernicus, but is now known to have no foundation in fact, being based on an error in Ptolemy's determination of precession.