The person who has the care of horses at an inn or stable; hence, any one who takes care of horses; a groom; -- so called because the innkeeper formerly attended to this duty in person.
A hostler, also spelled phonetically ostler, is a stableman, i.e. someone employed in a stable to take care of horses.http://www.etymonline.com/index.php?search=hostler&searchmode=none EtymologyOnLine- Hostler
A person who operates engines in engine house territory and works under the direction of the engine house foreman (inside hostler). Some railroads created outside hostlers after a limited exam, who could deliver engines anywhere in the terminal.