Select the most appropriate synonym of the given word.
Annul

The word 'Annul' means to declare invalid, nullify, or officially cancel a law, contract, or formal decision.
Let's check the options:

Invalidate: Make a document, contract, or claim invalid; nullify. (Synonym)

Uphold: Support, maintain, or confirm a legal ruling or decision. (Antonym)

Increase: Make or become greater in size or amount.

Create: Bring something into existence.

Hence, 'Invalidate' is the most appropriate synonym.