SQL> SELECT the_month
  2  FROM ( SELECT TO_CHAR( ADD_MONTHS( TRUNC(SYSDATE,'year')
  3                                   , LEVEL-1
  4                                   )
  5                       , 'Mon'
  6                       ) the_month
  7         FROM   dual
  8         CONNECT BY level <= 12
  9       )
 10  /

THE
---
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

12 rows selected.

SQL>

SELECT month FROM (
SELECT 'Jan' Month from dual union all
SELECT 'Feb' Month from dual union all
SELECT 'Mar' Month from dual union all
SELECT 'Apr' Month from dual union all
SELECT 'May' Month from dual union all
SELECT 'Jun' Month from dual union all
SELECT 'Jul' Month from dual union all
SELECT 'Aug' Month from dual union all
SELECT 'Sep' Month from dual union all
SELECT 'Oct' Month from dual union all
SELECT 'Nov' Month from dual union all
SELECT 'Dec' Month from dual);