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:

Month \Month\ (m[u^]nth), n. [OE. month, moneth, AS.
   m[=o]n[eth], m[=o]na[eth]; akin to m[=o]na moon, and to D.
   maand month, G. monat, OHG. m[=a]n[=o]d, Icel. m[=a]nu[eth]r,
   m[=a]na[eth]r, Goth. m[=e]n[=o][thorn]s. [root]272. See
   Moon.]
   One of the twelve portions into which the year is divided;
   the twelfth part of a year, corresponding nearly to the
   length of a synodic revolution of the moon, -- whence the
   name. In popular use, a period of four weeks is often called
   a month.
   [1913 Webster]

   Note: In the common law, a month is a lunar month, or
         twenty-eight days, unless otherwise expressed.
         --Blackstone. In the United States the rule of the
         common law is generally changed, and a month is
         declared to mean a calendar month. --Cooley's
         Blackstone.
         [1913 Webster]

   A month mind.
   (a) A strong or abnormal desire. [Obs.] --Shak.
   (b) A celebration made in remembrance of a deceased person a
       month after death. --Strype.

   Calendar months, the months as adjusted in the common or
      Gregorian calendar; April, June, September, and November,
      containing 30 days, and the rest 31, except February,
      which, in common years, has 28, and in leap years 29.

   Lunar month, the period of one revolution of the moon,
      particularly a synodical revolution; but several kinds are
      distinguished, as the synodical month, or period from
      one new moon to the next, in mean length 29 d. 12 h. 44 m.
      2.87 s.; the nodical month, or time of revolution from
      one node to the same again, in length 27 d. 5 h. 5 m. 36
      s.; the sidereal, or time of revolution from a star to
      the same again, equal to 27 d. 7 h. 43 m. 11.5 s.; the
      anomalistic, or time of revolution from perigee to
      perigee again, in length 27 d. 13 h. 18 m. 37.4 s.; and
      the tropical, or time of passing from any point of the
      ecliptic to the same again, equal to 27 d. 7 h. 43 m. 4.7
      s.

   Solar month, the time in which the sun passes through one
      sign of the zodiac, in mean length 30 d. 10 h. 29 m. 4.1
      s.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sidereal
    adj 1: of or relating to the stars or constellations; "sidereal
           bodies"; "the sidereal system"
    2: (of divisions of time) determined by daily motion of the
       stars; "sidereal time" [ant: civil]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "sidereal":
   Cynthian, anagalactic, asteroidal, astral, astrologic,
   astrologistic, astrologous, astronomic, astrophysical, celestial,
   circumplanetary, cislunar, empyreal, empyrean, equinoctial,
   extragalactic, galactic, heavenly, heliacal, intercosmic,
   interplanetary, intersidereal, interstellar, lunar, lunary, lunate,
   lunular, lunulate, meteoric, meteoritic, nebular, nebulose,
   nebulous, planetal, planetarian, planetary, planetesimal,
   semilunar, solar, sphery, star-spangled, star-studded, starry,
   stellar, stellary, terrestrial, uranic, zodiacal