Deathblow (noun)

1. A severe or fatal blow or setback.
2. An action or event that severely damages or destroys something or someone.

Origin:

Late 16th century: from death + blow.

Examples:

1. The company"s bankruptcy was a deathblow to the small town"s economy.
2. The loss of the key contract was a deathblow to the company.
3. The deathblow was the final punch that knocked out the boxer.
4. The deathblow was the last and fatal blow to the enemy.
5. The deathblow was the action that destroyed the enemy's army.