1
: for or during the entire night
He stayed overnight and went home the next day.
Let the paint dry overnight.
2
: very quickly or suddenly
The novel made her famous overnight.
1
: happening, traveling, or staying during the night
They went on an overnight bus trip.
an overnight train
Overnight guests are not allowed in the dormitory.
2
: happening very quickly or suddenly
The show was an overnight success.
Cite this Entry
“Overnight.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/overnight. Accessed 22 Jun. 2026.
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