noun

1. An unexpected occurrence; a surprise.

adjective

1. Happening quickly and with little or no warning.

   “The sudden drop in temperature left everyone cold and confused.”

2. Hastily prepared or employed; quick; rapid.

3. Hasty; violent; rash; precipitate.

Synonyms: abrupt, precipitous, subitaneous, hotheaded, impetuous, impulsive

adverb

1. Suddenly.