Source : Webster's Revised Unabridged Dictionary (1913)

Jewish calendar \Jew"ish cal"en*dar\
   A lunisolar calendar in use among Hebraic peoples, reckoning
   from the year 3761 b. c., the date traditionally given for
   the Creation.

   Note: It received its present fixed form from Hillel II.
         about 360 a. d. The present names of the months, which
         are Babylonian-Assyrian in origin, replaced older ones,
         Abib, Bul, etc., at the time of the Babylonian Exile.
         Nineteen years constitute a lunar cycle, of which the
         3d, 6th, 8th, 11th, 14th, 17th, and 19th years are leap
         years. The year 5663 [1902-3 a. d.] was the first year
         of the 299th lunar cycle. The common year is said to be
         defective, regular, or perfect (or abundant) according
         as it has 353, 354, or 355 days. The leap year has an
         intercalary month, and a total of 383 (defective), 384
         (regular), or 385 (perfect, or abundant) days. The
         calendar is complicated by various rules providing for
         the harmonious arrangement of festivals, etc., so that
         no simple perpetual calendar can be constructed. The
         following table gives the months in order, with the
         number of days assigned to each. Only three months vary
         in length. They are: Heshvan, which has 30 days in
         perfect years; Kislev, which has 30 days in regular and
         perfect years; and Adar, which has 30 days in leap
         years. The ecclesiastical year commences with Nisan and
         the civil year with Tishri. The date of the first of
         Tishri, or the Jewish New Year, is also given for the
         Jewish years 5661-5696 (1900-1935 a. d.). From these
         tables it is possible to transform any Jewish date into
         Christian, or vice versa, for the years 1900-1935 a. d.
         Months of the Jewish Year. 1 Tishri . . . . . . 30 2
         Heshvan . . . . . 29 (r. & d.) or 30 (p.) 3 Kislev . .
         . . . . 29 (d.) or 30 (r. & p.) 4 Tebet . . . . . . 29
         5 Shebat . . . . . . 30 6 Adar . . . . . . . 29 or 30
         (l.) -- Veadar . . . . . 29 (occuring only in leap
         years) 7 Nisan . . . . . . .30 8 Ivar . . . . . . ..29
         9 Sivan . . . . . . .30 10 Tammux . . . . . . 29 11 Ab
         . . . . . . . . 30 12 Elul . . . . . . ..29 Jewish Year
         a. d.

Source : WordNet®

Jewish calendar
     n : (Judaism) the calendar used by the Jews; dates from 3761 BC
         (the assumed date of the creation of the world); a lunar
         year of 354 days is adjusted to the solar year by
         periodic leap years [syn: {Hebrew calendar}]