一定
yídìng
surely; certainly; definitely; fixed; settled
In a story
我想:手机的主人一定很着急。I thought: whoever owns this must be worried sick.手机里的照片 · The Photos on the Phone · HSK 3
Grammar with 一定

Learn it in the app
Save a word while you read and it comes back as a flashcard, read aloud, when it is due.