[ pɒ'stɪlɪən ]
(also postillion )
■ noun a person who rides the leading nearside horse of a team or pair drawing a coach or carriage, when there is no coachman.
Origin
C16 (in the sense 'forerunner acting as guide to the post-horse rider'): from Fr. postillon , from Ital. postiglione 'post boy', from posta (see post 2 ).