This is the 5253rd most frequent Chinese word.
不見
"Not see" or "disappear."
不見 in this sentence describes the situation where the book is lost or misplaced.
我的书不见了。
My book is missing.
不見 here indicates that the subject 'he' cannot be seen, suggesting he is missing physically.
他不见了，大家都很着急。
He disappeared, and everyone was worried.
不見 in this context highlights the effect of the cold weather causing the leaves to disappear or shed.