"突然" (suddenly) is a Chinese adverb that means "without warning." It is commonly used to describe an event or action that occurs unexpectedly. The word comes from the Middle Chinese "tútjìen."

Example sentences in Engpsh:

The power went out suddenly in the middle of the night.
She suddenly reapzed she had forgotten her keys.

Example sentences in Chinese:

突然间，夜里停电了。
她突然发现她忘了带钥匙。