Its source is Yosef, a Hebrew name meaning "The Lord's addition (to the family)."
Josephus is a Latinate development of the original name Yosef. It was most notably used by the Jewish historian Josephus (c. 66 - c. 100).
His History of the Jewish War Against Rome is an important document, relating first-person accounts of ancient events. However, as a Jewish commander who surrendered to the Romans, then tried to persuade his fellow countrymen to give up, he is also one of history's notable turncoats.