SQL> create or replace procedure prc_test as
  2  begin
  3    dbms_output.put_line('Hello!');
  4  end;
  5  /

Procedure created.

SQL> grant execute on prc_test to mike;

Grant succeeded.

SQL> connect mike/lion@ora10
Connected.
SQL> create synonym prc_syn_test for scott.prc_test;

Synonym created.

SQL> set serveroutput on;
SQL> exec prc_syn_test;
Hello!

PL/SQL procedure successfully completed.

SQL>