In medieval astronomy, a spurious oscillatory motion of the equinoxes thought to have a period of 7,000 years. This concept, attributed to Thâbit ibn Qurra (c. 830-901), had a profound influence on medieval astronomy. In order to explain trepidation, Thâbit was said to have added a new sphere to the eight Ptolemaic spheres beyond the sphere of fixed stars.
From L. trepidationem "agitation, trembling," from trepidare "to tremble, hurry," from trepidus "anxious, scared;" cf. Skt. trprá- "hasty;" PIE base *trep- "to shake, tremble."
Larzeš, verbal noun of larzidan "to tremble, shiver;" Mid.Pers. larzidan "to shake, tremble;" Manichean Mid.Pers. rarz- "to shiver with fever;" Proto-Iranian *rarz- "to shake, tremble."