The Collaborative International Dictionary of English v.0.48:

Ostler \Ost"ler\, n.
   See Hostler.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ostler
    n 1: someone employed in a stable to take care of the horses
         [syn: stableman, stableboy, groom, hostler,
         ostler]