Meaning of “sudden” - Learner’s Dictionary

sudden

adjective us uk /ˈsʌdən/

B2 done or happening quickly and unexpectedly:

a sudden change/increase
His sudden death was a great shock to us all.

More examples

all of a sudden

B2 unexpectedly:

All of a sudden she got up and walked out.
suddenness noun [ U ]

(Definition of “sudden” from the Cambridge Learner’s Dictionary © Cambridge University Press)