- suddenly, all of a sudden, of a sudden - happening unexpectedly; "suddenly she felt a sharp pain in her side"
- abruptly, suddenly, short, dead - quickly and without warning; "he stopped suddenly"
Derived from adjective sudden1
- on the spur of the moment, suddenly - on impulse; without premeditation; "he decided to go to Chicago on the spur of the moment"; "he made up his mind suddenly"