moon (mo?on)n.1. often Moon The natural satellite of Earth, visible by reflection of sunlight and having a slightly elliptical orbit, approximately 363,100 kilometers (225,600 miles) distant at perigee and 405,700 kilometers (252,100 miles) at apogee. Its mean diameter is 3,475 kilometers (2,159 miles), its mass approximately one eightieth that of Earth, and its average period of revolution around Earth 29 days 12 hours 44 minutes calculated with respect to the sun.2. A natural satellite revolving around a planet.3. The moon as it appears at a particular time in its cycle of phases: a gibbous moon.4. A month, especially a lunar month.5. A disk, globe, or crescent resembling the natural satellite of Earth.6. Moonlight.7. Something unreasonable or unattainable: They acted as if we were asking for the moon.8. Slang The bared buttocks.v. mooned, moon·ing, moons v.intr.1. To wander about or pass time languidly and aimlessly.2. To yearn or pine as if infatuated.3. Slang To expose one’s buttocks in public as a prank or disrespectful gesture.v.tr. Slang To expose one’s buttocks to (others) as a prank or disrespectful gesture: “threatened to moon a passing … camera crew” (Vanity Fair).Idiom: over the moon In a state of great happiness.[Middle English mone, from Old English m?na; see m?- in Indo-European roots.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.moon (mu?n) n1. (Astronomy) (sometimes capital) the natural satellite of the earth. Diameter: 3476 km; mass: 7.35 × 1022 kg; mean distance from earth: 384 400 km; periods of rotation and revolution: 27.32 days. 2. (Astronomy) the face of the moon as it is seen during its revolution around the earth, esp at one of its phases: new moon; full moon. 3. (Astronomy) any natural satellite of a planet4. (Astronomy) moonlight; moonshine5. something resembling a moon6. (Astronomy) a month, esp a lunar one7. once in a blue moon very seldom8. over the moon informal extremely happy; ecstatic9. reach for the moon to desire or attempt something unattainable or difficult to obtainvb10. (when: tr, often foll by away; when intr, often foll by around) to be idle in a listless way, as if in love, or to idle (time) away11. (intr) slang to expose one’s buttocks to passers-by[Old English m?na; compare Old Frisian m?na, Old High German m?no] ?moonless adjMoon (mu?n) n (Linguistics) a system of embossed alphabetical signs for blind readers, the fourteen basic characters of which can, by rotation, mimic most of the letters of the Roman alphabet, thereby making learning easier for those who learned to read before going blind. Compare Braille1Moon (mu?n) n (Biography) William. 1818?94, British inventor of the Moon writing system in 1847, who, himself blind, taught blind children in Brighton and printed mainly religious works from stereotyped plates of his own designingCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014moon (mun) n. 1. the earth’s natural satellite, orbiting the earth at a mean distance of 238,857 miles (384,393 km) and having a diameter of 2160 miles (3476 km). 2. this body during a particular lunar month, or during a certain period of time, or at a certain point of time, regarded as a distinct object or entity. 3. a lunar month, or, in general, a month. 4. any planetary satellite: the moons of Jupiter. 5. something shaped like an orb or a crescent. 6. moonlight. v.i. 7. to act or wander abstractedly, listlessly, or dreamily: to moon about all day. 8. to sentimentalize or remember nostalgically. 9. Slang. to expose one’s buttocks suddenly and publicly as a prank or gesture of disrespect. v.t. 10. to spend (time) idly: to moon the afternoon away. [before 900; Middle English mone, Old English m?na; c. Old Frisian m?na, Old Saxon, Old High German m?no, Old Norse m?ni, Gothic mena; akin to Latin m?nsis month, Greek m?n? moon, m?n month, Skt m?sa moon, month] moon?er, n. moon?less, adj. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.moonHalf of the moon is always in sunlight, as seen on the left. The relative positions of Earth, the moon, and the sun determine how much of the lighted half can be seen from Earth, as seen on the right. These forms in which the moon appears are known as phases.moon (mo?on)1. Often Moon The natural satellite of Earth, visible by reflection of sunlight and traveling around Earth in a slightly elliptical orbit at an average distance of about 237,000 miles (381,500 kilometers). The moon’s average diameter is 2,160 miles (3,475 kilometers), and its mass is about 1/80 that of Earth.2. A natural satellite revolving around a planet: the moons of Jupiter.3. The moon as it appears at a particular time in its cycle of phases: a half moon.Did You Know? We earthlings usually think of our moon as the moon, but any planet’s natural satellites are properly called moons. Jupiter has at least 28 moons, while Saturn has 30, and additional small ones around these and other planets may yet be discovered. Earth’s moon is also not necessarily typical of other moons in the solar system. No water exists on our moon, but some scientists think that one of Jupiter’s moons, Europa, may have liquid water that might support life under a thick layer of ice. Titan, a moon of Saturn, is also thought to have an environment that can support primitive life: an ocean of ethane instead of water. Earth’s moon is also very quiet, geologically. By comparison, Io, another of Jupiter’s moons, is a violent cauldron of geologic activity. It is covered with huge volcanoes that emit plumes of sulfur so enormous that they can be seen by the Hubble Space Telescope orbiting Earth.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.MoonSee also astronomy; planets; sun. selenographythe branch of astronomy that deals with the charting of the moon?s surface. ? selenographer, selenographist, n. ? selenographic, selenographical, adj.selenolatrythe worship of the moon.selenologythe branch of astronomy that studies the physical characteristics of the moon. ? selenologist, n. ? selenological, adj.selenomancya form of divination involving observation of the moon.-Ologies & -Isms. Copyright 2008 The Gale Group, Inc. All rights reserved.