outrunner

noun4

1. •
   One who outruns.
2. •
   An electric motor having the rotor outside the stator.
3. •
   A person or animal who accompanies a vehicle or procession but who is not seated in the vehicle or part of the procession.

   • The outrunner of the Khedevial carriage comes along and the man on the box is silent, perhaps two outrunners speed ahead of the prancing horses clearing the way for the royal cortege. — 1909
4. •
   An offshoot; a branch.

   • some out-runner of the river, where the streams run not strongly — 1620