1. a fierce or destructive attack: "a series of onslaughts on the citadel"
▪ a large quantity of people or things that is difficult to cope with:"an onslaught of electronic mail"
Word Originearly 17th century (also in the form anslaight): from Middle Dutch aenslag, from aen ‘on’ + slag ‘blow’. The change in the ending was due to association with (now obsolete) slaught ‘slaughter’.