The knife we know but in the 14c the word was slang, 'a word of the vulgar tongue'. Henry Knighton (d. 1396) described in quiet shock the appearance of several ladies at a *tournament, all dressed brightly as men, with daggers 'across their bellies in a pouch'. [< OldFr. dague = a long point]
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.