1. a fierce or destructive attack
2. an overwhelmingly large quantity of people or things coming at once

Examples

• The enemy launched a fierce onslaught at dawn.
• The castle walls crumbled under the onslaught of cannon fire.
• She faced an onslaught of criticism from the media.
• The store prepared for the onslaught of holiday shoppers.
• The team couldn’t withstand the onslaught of their opponents.
• An onslaught of emails flooded his inbox after the announcement.
• The coastal town braced for the onslaught of the hurricane.