expression, godan verb (-ru)
Used to indicate denial, refusal, or disagreement. Often implies a side-to-side motion. Compare with 頭を振る, which can also mean shaking the head in a broader sense.
See also: 頭を振る
彼は何も言わずに首を振った。
He shook his head without saying anything.
I could only shake my head at that proposal.