Sentence:  The small cross-bow, called the arbalet or arbalest, is said to have been invented by the Sicilians. It was carried by the foot-soldiers, and when used was charged with a <WSD>quarrel</WSD> or bar-bolt, that is, a small arrow with a flat head, one of which occasioned the death of Harold at the battle of Hastings,nb.... 
Meaning of the word marked with <WSD> tags:  A square-headed arrow for a crossbow.