There are a plethora of synonyms for the term "unforeseen attack". Some of them include ambush, surprise attack, sudden strike, sneak attack, unprovoked assault, and unexpected onslaught. These synonyms all describe a sudden and unexpected attack carried out by an individual or group. Ambush and surprise attacks both suggest an element of deception, while sudden strikes and unexpected onslaughts imply no warning whatsoever. Unprovoked assault and sneak attack both suggest an element of aggression on the part of the attacker. Regardless of the specific term used, an unforeseen attack is always a dangerous and unsettling event that can have serious consequences.