An Etymological Dictionary of Astronomy and Astrophysics

1. A large, solid-hoofed, herbivorous quadruped, Equus caballus, domesticated since prehistoric times.
   

2. In a → planispheric astrolabe, the small prominence that, inserted into a slit in the pin, prevents the parts of the instrument from coming loose when in use. The part owes its name to the fact that astrolabe-makers would often shape it into a horse’s head (online museo galileo, VirtualMuseum).
   

See also:

→ horse latitude, → Horsehead Nebula, → horsepower, → horseshoe mounting, → horseshoe orbit.

Etymology (EN): Horse, O.E. hors, from P.Gmc. *khursa- (cf. M.Du. ors, Du. ros, O.H.G. hros, Ger. Roß “horse”), of unknown origin; → latitude.

Etymology (PE): Asb “horse,” from Mid.Pers. asp; O.Pers. asa- “horse;” Av. aspa- “horse,” aspā- “mare,” aspaiia- “pertaining to the horse;” cf. Skt. áśva- “horse, steed;” Gk. hippos;
L. equus; O.Ir. ech; Goth. aihwa-; O.E. eoh “horse;” PIE base *ekwo- “horse.”