pillion
Concise Oxford English Dictionary © 2008 Oxford University Press:
pillion/ˈpɪliən/
▶noun
- 1 a seat for a passenger behind a motorcyclist.
- 2 historical a woman's light saddle.
■ a cushion attached to the back of a saddle for an additional passenger.
– origin C15: from Sc. Gaelic pillean, Ir. pillín ‘small cushion’, dimin. of pell, from L. pellis ‘skin’.
'pillion' also found in these Oxford entries:

