Source : Webster's Revised Unabridged Dictionary (1913)

Moon \Moon\, n. [OE. mone, AS. m[=o]na; akin to D. maan, OS. &
   OHG. m[=a]no, G. mond, Icel. m[=a]ni, Dan. maane, Sw.
   m[*a]ne, Goth. m[=e]na, Lith. men?, L. mensis month, Gr. ?
   moon, ? month, Skr. m[=a]s moon, month; prob. from a root
   meaning to measure (cf. Skr. m[=a] to measure), from its
   serving to measure the time. [root]271. Cf. {Mete} to
   measure, {Menses}, {Monday}, {Month}.]
   1. The celestial orb which revolves round the earth; the
      satellite of the earth; a secondary planet, whose light,
      borrowed from the sun, is reflected to the earth, and
      serves to dispel the darkness of night. The diameter of
      the moon is 2,160 miles, its mean distance from the earth
      is 240,000 miles, and its mass is one eightieth that of
      the earth. See {Lunar month}, under {Month}.

            The crescent moon, the diadem of night. --Cowper.

   2. A secondary planet, or satellite, revolving about any
      member of the solar system; as, the moons of Jupiter or
      Saturn.

   3. The time occupied by the moon in making one revolution in
      her orbit; a month. --Shak.

   4. (Fort.) A crescentlike outwork. See {Half-moon}.

   {Moon blindness}.
      (a) (Far.) A kind of ophthalmia liable to recur at
          intervals of three or four weeks.
      (b) (Med.) Hemeralopia.

   {Moon dial}, a dial used to indicate time by moonlight.

   {Moon face}, a round face like a full moon.

   {Moon madness}, lunacy. [Poetic]

   {Moon month}, a lunar month.

   {Moon trefoil} (Bot.), a shrubby species of medic ({Medicago
      arborea}). See {Medic}.

   {Moon year}, a lunar year, consisting of lunar months, being
      sometimes twelve and sometimes thirteen.

Source : WordNet®

moon blindness
     n 1: inability to see clearly in dim light; due to a deficiency
          of vitamin A or to a retinal disorder [syn: {nyctalopia},
           {night blindness}]
     2: recurrent eye inflammation in horses; sometimes resulting in
        blindness [syn: {mooneye}]