onslaught (n.) Look up onslaught at Dictionary.com
1620s, anslaight, somehow from or on analogy of Dutch aanslag "attack," from Middle Dutch aenslach, from aen "on" (see on) + slach "blow," related to slaen "slay." Spelling influenced by obsolete (since c.1400) English slaught (n.) "slaughter," from Old English sleaht (see slaughter (n.)). No record of its use in 18c.; apparently revived by Scott.