Explanation:

- Option 1: Brusque

- This word means abrupt or offhand in speech or manner.

- It is spelt correctly.

- Option 2: Boisterous

- This means noisy, energetic, and cheerful.

- The spelling is correct.

- Option 3: Blizard

- This is incorrectly spelt. The correct spelling is "blizzard."

- It refers to a severe snowstorm with strong winds.

- Option 4: Blonde

- Refers to a person with fair hair.

- The spelling is correct.

The incorrectly spelt word is:

Option 3: Blizard

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