Definition of "pilum"

Besides a lighter spear, the Roman legionary grasped in his right hand the formidable pilum, a ponderous javelin whose utmost length was about six feet and which was terminated by a massy triangular point of steel of about eighteen inches.

1776, Edward Gibbon, The History of the Decline and Fall of the Roman Empire, Penguin 2000, page 21

Verica plucked a pilum from the hands of the nearest legionary – the soldier didn't react – and handed it to me.

2011, Ben Aaronovitch, Rivers of London, Gollancz 2011, page 371