An onslaught on someone or something is a very violent, forceful attack against them. The rebels responded to a military onslaught against them by launching a major assault on an army camp. = assault
If you refer to an onslaught of something, you mean that there is a large amount of it, often so that it is very difficult to deal with. the constant onslaught of ads on American TV. = barrage
the rapid and continuous delivery of linguistic communication (spoken or written)
onslaughts
Pronunciation
Etymology
[ 'än-"slot, 'on- ] (noun.) circa 1625. modification of Dutch aanslag act of striking; akin to Old English an on and to Old English slEan to strike; more at SLAY.