Moon (m?n), n. [OE. mone, AS. mōna; akin to D. maan, OS. & OHG. māno, G. mond, Icel. māni, Dan. maane, Sw. måne, Goth. mēna, Lith. menů, L. mensis month, Gr. mh`nh moon, mh`n month, Skr. mās moon, month; prob. from a root meaning to measure (cf. Skr. mā to measure), from its serving to measure the time. √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.

Moon , v. i. To act if moonstruck; to wander or gaze about in an abstracted manner.

Elsley was mooning down the river by himself. C. Kingsley.

Moon , v. t. [imp. & p. p. Mooned (?); p. pr. & vb. n.Mooning.] To expose to the rays of the moon.

If they have it to be exceeding white indeed, they seethe it yet once more, after it hath been thus sunned and mooned. Holland.

-- Webster's unabridged 1913