The Collaborative International Dictionary of English v.0.48:

Sidereal \Si*de"re*al\, a. [L. sidereus, from sidus, sideris, a
   constellation, a star. Cf. Sideral, Consider, Desire.]
   1. Relating to the stars; starry; astral; as, sidereal
      astronomy.
      [1913 Webster]

   2. (Astron.) Measuring by the apparent motion of the stars;
      designated, marked out, or accompanied, by a return to the
      same position in respect to the stars; as, the sidereal
      revolution of a planet; a sidereal day.
      [1913 Webster]

   Sidereal clock, day, month, year. See under Clock,
      Day, etc.

   Sideral time, time as reckoned by sideral days, or, taking
      the sidereal day as the unit, the time elapsed since a
      transit of the vernal equinox, reckoned in parts of a
      sidereal day. This is, strictly, apparent sidereal time,
      mean sidereal time being reckoned from the transit, not of
      the true, but of the mean, equinoctial point.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Year \Year\, n. [OE. yer, yeer, [yogh]er, AS. ge['a]r; akin to
   OFries. i?r, g?r, D. jaar, OHG. j[=a]r, G. jahr, Icel. [=a]r,
   Dan. aar, Sw. [*a]r, Goth. j?r, Gr. ? a season of the year,
   springtime, a part of the day, an hour, ? a year, Zend
   y[=a]re year. [root]4, 279. Cf. Hour, Yore.]
   [1913 Webster]
   1. The time of the apparent revolution of the sun trough the
      ecliptic; the period occupied by the earth in making its
      revolution around the sun, called the astronomical year;
      also, a period more or less nearly agreeing with this,
      adopted by various nations as a measure of time, and
      called the civil year; as, the common lunar year of 354
      days, still in use among the Mohammedans; the year of 360
      days, etc. In common usage, the year consists of 365 days,
      and every fourth year (called bissextile, or leap year) of
      366 days, a day being added to February on that year, on
      account of the excess above 365 days (see Bissextile).
      [1913 Webster]

            Of twenty year of age he was, I guess. --Chaucer.
      [1913 Webster]

   Note: The civil, or legal, year, in England, formerly
         commenced on the 25th of March. This practice continued
         throughout the British dominions till the year 1752.
         [1913 Webster]

   2. The time in which any planet completes a revolution about
      the sun; as, the year of Jupiter or of Saturn.
      [1913 Webster]

   3. pl. Age, or old age; as, a man in years. --Shak.
      [1913 Webster]

   Anomalistic year, the time of the earth's revolution from
      perihelion to perihelion again, which is 365 days, 6
      hours, 13 minutes, and 48 seconds.

   A year's mind (Eccl.), a commemoration of a deceased
      person, as by a Mass, a year after his death. Cf. A
      month's mind, under Month.

   Bissextile year. See Bissextile.

   Canicular year. See under Canicular.

   Civil year, the year adopted by any nation for the
      computation of time.

   Common lunar year, the period of 12 lunar months, or 354
      days.

   Common year, each year of 365 days, as distinguished from
      leap year.

   Embolismic year, or Intercalary lunar year, the period of
      13 lunar months, or 384 days.

   Fiscal year (Com.), the year by which accounts are
      reckoned, or the year between one annual time of
      settlement, or balancing of accounts, and another.

   Great year. See Platonic year, under Platonic.

   Gregorian year, Julian year. See under Gregorian, and
      Julian.

   Leap year. See Leap year, in the Vocabulary.

   Lunar astronomical year, the period of 12 lunar synodical
      months, or 354 days, 8 hours, 48 minutes, 36 seconds.

   Lunisolar year. See under Lunisolar.

   Periodical year. See Anomalistic year, above.

   Platonic year, Sabbatical year. See under Platonic, and
      Sabbatical.

   Sidereal year, the time in which the sun, departing from
      any fixed star, returns to the same. This is 365 days, 6
      hours, 9 minutes, and 9.3 seconds.

   Tropical year. See under Tropical.

   Year and a day (O. Eng. Law), a time to be allowed for an
      act or an event, in order that an entire year might be
      secured beyond all question. --Abbott.

   Year of grace, any year of the Christian era; Anno Domini;
      A. D. or a. d.
      [1913 Webster] year 2000 bug

WordNet (r) 3.0 (2006):

year
    n 1: a period of time containing 365 (or 366) days; "she is 4
         years old"; "in the year 1920" [syn: year, twelvemonth,
         yr]
    2: a period of time occupying a regular part of a calendar year
       that is used for some particular activity; "a school year"
    3: the period of time that it takes for a planet (as, e.g.,
       Earth or Mars) to make a complete revolution around the sun;
       "a Martian year takes 687 of our days"
    4: a body of students who graduate together; "the class of '97";
       "she was in my year at Hoehandle High" [syn: class, year]

The Devil's Dictionary (1881-1906):

YEAR, n.  A period of three hundred and sixty-five disappointments.