Adar Ri·shon 
(rē-shōn)
(rē-shōn)n.
An intercalary month in the Jewish calendar, added in leap years before the regular month of Adar. See Table at calendar.
[Hebrew 'ădār ri'šôn, first Adar : 'ădār, Adar; see ADAR + ri'šôn, first; akin to rō'š, head, top, beginning; see ROSH HASHANAH.]