Frequency: The word is one of the 3000 most common words in English.
1.
Sudden means happening quickly and unexpectedly.
He had been deeply affected by the ~ death of his father-in-law...
She started to thank him, but a ~ movement behind him caught her attention...
It was all very ~.
ADJ: usu ADJ n
~ness
The enemy seemed stunned by the ~ness of the attack.
N-UNCOUNT: oft the N of n
2.
If something happens all of a ~, it happens quickly and unexpectedly.
All of a ~ she didn’t look sleepy any more.
PHRASE: usu PHR with cl, PHR with v