plural moons
1
or the Moon
: the large round object that circles the Earth and that shines at night by reflecting light from the sun
The telescope makes the craters on the surface of the moon incredibly clear.
The moon isn't out tonight. = There's no moon tonight. [=the moon cannot be seen tonight]
the first moon [=lunar] landing [=the first time people landed a spacecraft on the moon]
the orbit of the Moon around the Earth
2
: a large round object like the moon that circles around a planet other than the Earth
Europa and Io are both moons of Jupiter.
a planet orbited by one moon
moons; mooned; mooning
informal
: to bend over and show your bare buttocks to someone as a rude joke or insult
One of the boys mooned the crowd.
One of the boys mooned at the crowd.
Cite this Entry
“Moon.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/moon. Accessed 16 Apr. 2026.
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