moon

¹

[moon]

noun

1. none the moon or the Moon the earth's natural satellite, orbiting the earth at a mean distance of 238,857 miles (384,393 km) and having a diameter of 2,160 miles (3,476 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.

7. a platyfish.

8. Slang.,  the buttocks, especially when bared.

verb (used without object)

1. to act or wander abstractedly or listlessly.

   You've been mooning about all day.

2. to sentimentalize or remember nostalgically.

   He spent the day mooning about his lost love.

3. to gaze dreamily or sentimentally at something or someone.

   They sat there mooning into each other's eyes.

4. Slang.,  to expose one's buttocks suddenly and publicly as a prank or gesture of disrespect.

verb (used with object)

1. to spend (time) idly.

   She mooned the afternoon away, unable to think what to do next.

2. to illuminate by or align against the moon.

3. Slang.,  to expose one's buttocks to as a prank or gesture of disrespect.

Moon

²

[moon]

noun

1. Sun Myung 1920–2012, Korean religious leader: founder of the Unification Church.

Moon

¹

/ muːn /

noun

1. 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 Braille 1

Moon

²

/ muːn /

noun

1. 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 designing

moon

³

/ muːn /

noun

1. (sometimes capital) the natural satellite of the earth. Diameter: 3476 km; mass: 7.35 × 10 ²² kg; mean distance from earth: 384 400 km; periods of rotation and revolution: 27.32 days

2. 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. any natural satellite of a planet

4. moonlight; moonshine

5. something resembling a moon

6. a month, esp a lunar one

7. very seldom

8. informal,  extremely happy; ecstatic

9. to desire or attempt something unattainable or difficult to obtain

verb

1. to be idle in a listless way, as if in love, or to idle (time) away

2. slang,  (intr) to expose one's buttocks to passers-by

moon

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 381,600 km (237,000 mi). The Moon's average diameter is 3,480 km (2,160 mi), and its mass is about 1/80 that of Earth. Its average period of revolution around Earth is 29 days, 12 hours, 44 minutes.

2. See more at giant impact theory

3. A natural satellite revolving around a planet.

moon

1. A natural satellite of a planet; an object that revolves around a planet. The planets vary in the number of their moons; for example, Mercury and Venus have none, the Earth has one, and Jupiter has seventeen or more. The planets' moons, like the planets themselves, shine by reflected light.

The Earth's moon is about 240,000 miles away and is about 2,000 miles in diameter. The volume of the Earth is fifty times that of the moon; the mass of the Earth is about eighty times that of the moon. The moon has no atmosphere, and its gravity is about one-sixth that of the Earth.

Other Word Forms

• mooner noun
• moonless adjective

Word History and Origins

Origin of moon¹

First recorded before 900; Middle English mone, Old English mōna; cognate with Old High German māno, Old Norse māni, Gothic mena; akin to German Mond “moon,” Latin mēnsis “month,” Greek mḗnē “moon,” Sanskrit māsa “moon, month”

Word History and Origins

Origin of moon¹

Old English mōna; compare Old Frisian mōna, Old High German māno

A Closer Look

The Earth's Moon is a desolate and quiet place. The only natural satellite of Earth, it consists almost entirely of rock, shows no signs of ongoing geologic activity, has no water, and has a very thin atmosphere consisting primarily of sodium. But our Moon does not present a typical case for planetary satellites. Over the last 50 years, over a hundred more moons have been discovered in the solar system, so that they now total 165, nearly all of them orbiting the larger planets Jupiter, Saturn, and Uranus (Mercury and Venus have no moon), with an additional four moons orbiting dwarf planets. Because they are so far from the Sun, these moons are for the most part extremely cold. Io, one of Jupiter's 63 known moons, is an exception. It is the most geologically active body in the solar system, with almost constant volcanic activity and a surface covered by cooling lava. Some scientists think that another moon of Jupiter, Europa, may have liquid water capable of supporting life underneath a thick layer of surface ice. Titan, one of Saturn's moons, may also be capable of supporting primitive life in the ocean of liquid methane on its frigid surface.

Idioms and Phrases

Idioms

1. over the moon. over the moon.

2. blue moon. blue moon.

see ask for the moon; once in a blue moon.

Example Sentences

"I'm over the moon that we got picked to trial this out. You can't fault the heating system – it is a 100% improvement on what we had before."

Read more on BBC

Danger feels suspended in the soft-blue light, in which the lion’s tail and the round, silvery moon, balanced just-so, are poised like a raised mallet and gong.

Read more on The Wall Street Journal

In early 2026, Blue Origin is looking to launch a company cargo craft to the moon, aiming to land the ship on the lunar surface.

Read more on The Wall Street Journal

"I am overwhelmed... I don't know what words to use, but I am over the moon."

Read more on Barron's

In March, the company became the first to launch a commercial lander upright and intact on the moon’s surface.

Read more on MarketWatch