noun
pillion
PIL-ee-un/pˈɪljʌn/
A seat behind the main rider on a motorcycle or horse.
The motorcycle has a padded pillion just behind the rider.

Etymology
Latin pellis, “skin” or “pelt,” underlies this Celtic-origin word for a light saddle. Its meaning expanded to a pad behind a saddle for a second person—the seating arrangement preserved in the cycle sense.
More examples
- She climbs onto the pillion and holds the rider's waist.
- This motorcycle's narrow pillion leaves little room for a passenger.
- The horse carries a second rider on a pillion.
Forms
pillion · pillions
Similar words
- seat
- A broader term that does not specify position behind a rider.