General antonyms:
* Unofficial: This is the most direct opposite, meaning something not authorized or recognized.
* Informal: This implies a lack of formality or structure.
* Unrecognized: This means not acknowledged or accepted.
* Amateur: This refers to something done by someone who is not a professional.
More specific antonyms:
* Unorthodox: This means not conforming to accepted standards or practices.
* Personal: This refers to something done by an individual, not a group or organization.
* Private: This means something not open to the public.
* Unpublished: This refers to something not released to the public.
Example:
* Official: The official website of the company.
* Unofficial: The unofficial fan website of the band.
Ultimately, the best antonym for "official" depends on the specific meaning you want to convey.