Found 2 items, similar to blue moon.
English → English (WordNet) Definition: blue moon blue moon n : a long time; “something that happens once in blue moon almost never happens”
English → English (gcide) Definition: blue moon Moon \Moon\ (m[=oo]n), 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[*u], L. mensis month, Gr. mh`nh moon, mh`n 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. [1913 Webster] The crescent moon, the diadem of night. --Cowper. [1913 Webster] 2. A secondary planet, or satellite, revolving about any member of the solar system; as, the moons of Jupiter or Saturn. [1913 Webster] 3. The time occupied by the moon in making one revolution in her orbit; a month. --Shak. [1913 Webster] 4. (Fort.) A crescentlike outwork. See Half-moon. [1913 Webster] 5. The deliberately exposed naked buttocks. [slang] [PJC] 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. blue moon, see blue moon in the vocabulary. [1913 Webster] blue moon \blue moon"\ The second full moon occurring in the same month; -- derived from the expression once in a blue moon; as, we had a blue moon on January 31, 1999, and another in March. [PJC] once in a blue moon very rarely; -- from the observation that the moon rarely has a bluish tint. Note: In 1980, the phrase blue moon was applied to the second full moon of any month, because this phenomenon is unusual. This new meaning for the old phrase blue moon has become widely accepted. [PJC]