1  –  COMMENT IS string

    This clause can be used to add several lines of comment to the
    synonym object. The SHOW SYNONYM statement displays the comment.

    This clause is equivalent to the COMMENT ON SYNONYM statement.

2  –  FOR object-name

    You may change the synonym to reference a different database
    object; however, it must be of the same type. Oracle Rdb assumes
    that the object has the same or similar characteristics as
    the referenced object. The referenced object must exist in the
    database.

3  –  synonym-name

    The name of an existing synonym you want to alter.