expression, godan verb (-ru)
hang oneself; hang by the neck
Refers to suicide by hanging or, less commonly, to hanging someone else. The phrase is a fixed expression using 首 (neck) and 吊る (to hang).
彼は絶望して首を吊った。
He hanged himself in despair.
首を吊るなんて考えてはいけない。
You mustn't think of hanging yourself.