The Collaborative International Dictionary of English v.0.48:

Julian \Jul"ian\ (?; 277) a. [L. Julianus, fr. Julius. Cf.
   July, Gillian.]
   Relating to, or derived from, Julius Caesar.
   [1913 Webster]

   Julian calendar, the calendar as adjusted by Julius Caesar,
      in which the year was made to consist of 365 days, each
      fourth year having 366 days.

   Julian epoch, the epoch of the commencement of the Julian
      calendar, or 46 b. c.

   Julian period, a chronological period of 7,980 years,
      combining the solar, lunar, and indiction cycles (28 x 19
      x 15 = 7,980), being reckoned from the year 4713 B. C.,
      when the first years of these several cycles would
      coincide, so that if any year of the period be divided by
      28, 19, or 15, the remainder will be the year of the
      corresponding cycle. The Julian period was proposed by
      Scaliger, to remove or avoid ambiguities in chronological
      dates, and was so named because composed of Julian years.


   Julian year, the year of 365 days, 6 hours, adopted in the
      Julian calendar, and in use until superseded by the
      Gregorian year, as established in the reformed or
      Gregorian calendar.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Calendar \Cal"en*dar\, n. [OE. kalender, calender, fr. L.
   kalendarium an interest or account book (cf. F. calendrier,
   OF. calendier) fr. L. calendue, kalendae, calends. See
   Calends.]
   1. An orderly arrangement of the division of time, adapted to
      the purposes of civil life, as years, months, weeks, and
      days; also, a register of the year with its divisions; an
      almanac.
      [1913 Webster]

   2. (Eccl.) A tabular statement of the dates of feasts,
      offices, saints' days, etc., esp. of those which are
      liable to change yearly according to the varying date of
      Easter.
      [1913 Webster]

   3. An orderly list or enumeration of persons, things, or
      events; a schedule; as, a calendar of state papers; a
      calendar of bills presented in a legislative assembly; a
      calendar of causes arranged for trial in court; a calendar
      of a college or an academy.
      [1913 Webster]

   Note: Shepherds of people had need know the calendars of
         tempests of state. --Bacon.
         [1913 Webster]

   Calendar clock, one that shows the days of the week and
      month.

   Calendar month. See under Month.

   French Republican calendar. See under Vend['e]miaire.

   Gregorian calendar, Julian calendar, Perpetual
   calendar. See under Gregorian, Julian, and Perpetual.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Julian calendar
    n 1: the solar calendar introduced in Rome in 46 b.c. by Julius
         Caesar and slightly modified by Augustus, establishing the
         12-month year of 365 days with each 4th year having 366
         days and the months having 31 or 30 days except for
         February [syn: Julian calendar, Old Style calendar]