An unexpected occurrence; a surprise.
"The sudden arrival of our old friend completely surprised everyone at the party."
"The sudden caught everyone off guard when the lights went out without warning."
happening without warning or in a short space of time
"a sudden storm"
"a sudden decision"
"a sudden cure"
Happening quickly and with little or no warning.
"The sudden thunderstorm caught everyone off guard as they were still outside without an umbrella."
In plain English: Sudden means something happens very quickly and without any warning beforehand.
"The sudden noise made everyone jump out of their seats."
Usage: Use sudden to describe events that happen rapidly without prior notice, such as a sudden storm or a sudden realization. Avoid confusing it with "abrupt," which implies an intentional break in continuity rather than mere lack of warning.
Suddenly.
"The sudden noise startled everyone in the room."
The word "sudden" comes from Latin subitus, which literally meant something that had come or gone stealthily under cover. It entered Middle English via Anglo-Norman and Old French to describe events happening immediately, eventually replacing the native Old English term for a fleeting occurrence.