If you're talking about expressing something:
* Suppress: To hold back or restrain.
* Conceal: To hide or keep secret.
* Withhold: To refrain from giving or revealing.
* Silence: To make quiet or stop from speaking.
If you're talking about a method of transportation:
* Slow: Moving at a low speed.
* Leisurely: Done at a relaxed and unhurried pace.
* Local: Relating to or restricted to a particular place.
If you're talking about a mail service:
* Ordinary: Not express, regular.
* Standard: Not express, the usual method.
Other possible antonyms:
* Implied: Suggested but not stated directly.
* Indirect: Not straightforward or explicit.
* Vague: Not clear or precise.
To give you the most accurate antonym, please provide more context about how you're using the word "express."