Dictionary.net

• v[=e]'a-dar, n. the name of the intercalary or thirteenth month of the Jewish year, which must have been inserted about every third year. [Heb., 'the additional adar,' from ve, and, and adar, so called because it was introduced in the calendar after the month Adar.]

1908 - Chambers's Twentieth Century Dictionary of the English Language
By Thomas Davidson