All of a sudden' is an idiomatic expression used to describe something that happens ABRUPTLY or without warning. The crossword solutions for this term are BAM, ABRUPTLY, BANG, WHAMMO, and ONSHORTNOTICE. BAM is an onomatopoeia used to describe a loud sound, while BANG is another onomatopoeia used to describe a loud explosion or impact. ABRUPTLY means suddenly and unexpectedly, and WHAMMO is a slang term used to emphasize the suddenness of an action. Finally, ONSHORTNOTICE means without much advance warning.