Definition for "All of a sudden"

all at once (without warning) "all at once, he started shouting"

of a sudden (happening unexpectedly) "suddenly she felt a sharp pain in her side"

....Source from : wordnetweb

set phrase, colloquial Suddenly, quickly.

All of a sudden I felt very hot and tired.

....Source from : Wiktionary

1. without warning; "all at once, he started shouting"

2. suddenly: happening unexpectedly; "suddenly she felt a sharp pain in her side"

3. All of a Sudden was singer-songwriter John Hiatt's fifth album, released in 1982. It was his first of three albums with Geffen Records.

4. Suddenly, quickly

....Source from : Google Definitions