aanslag

Dutch aanslag means 'a striking at' — from aan ('on') and slag ('a blow' or 'strike'). The word entered English in the early 1600s, likely through military contact during the Dutch Revolt against Spain (1568-1648). English and Dutch soldiers fought alongside each other, and military vocabulary flowed freely between the two Germanic languages. English also borrowed 'furlough,' 'knapsack,' and 'landscape' from Dutch during this period.

The original Dutch word had a broader meaning than pure military attack. Aanslag could mean an attempt, an undertaking, or a tax assessment — any 'striking' in a figurative sense. English narrowed it. By the mid-1600s, onslaught meant a violent, overwhelming assault and nothing else. The attempt became the attack. The blow became the bombardment.

The spelling shifted from 'onslaught' to its current form by the 1700s, possibly influenced by the English word 'slaughter.' The 'slaught' ending looks like it should be related to 'slaughter,' and this false association may have pushed the meaning further toward violence. Etymology sometimes works through sound — if a word sounds like it should mean something destructive, it starts meaning something destructive.

Onslaught is now used freely outside military contexts. A media onslaught. An onslaught of emails. An onslaught of winter weather. The word carries a permanent sense of being overwhelmed — not just attacked, but attacked from a direction and with a force you cannot withstand. The Dutch blow has become an English avalanche.