adverb
without prior notice; without warning
Used when something happens suddenly, without any advance notification. Often appears in formal or written contexts, such as service changes, cancellations, or unexpected events.
イベントは予告なく中止になることがあります。
The event may be canceled without prior notice.
予告なく仕様が変更される場合があります。
Specifications may change without notice.
Compound of 予告 (advance notice) + なく (adverbial form of ない, 'without').