From the Latin verb jactare, meaning to throw or to throw out, and picked up by the French, Jactance, meaning vaingloriously boasting.  

2 hours ago, Bill W said:

The earliest known usage of jactance was during the Middle English period, between 1150-1500.  The earliest OED evidence for the word was before 1492 in a translation by William Caxton, a printer, merchant, and diplomat.   

Caxton is probably best know for his printing press, which he set up in Westminster. It is believed to be the first printing press in England. Among the books he published were works that he had translated into English himself.