Revoke

Revokes access privileges from a user, a group, or all users.

REVOKE privilege [, ...]
    ON object [, ...]
    FROM { PUBLIC | GROUP groupname | username }

Use REVOKE to remove privileges to an object of which you are the owner. You can revoke privileges from a specific user, from a group, or from all users (by specifying the PUBLIC keyword).

The following example revokes INSERT privileges on the books table from a user guest:

booktown=# REVOKE INSERT ON guest FROM books;
CHANGE