(~s)
1.
A ~ is a telephone call that you can book through an operator or at a hotel to make sure that you wake up at a particular time.
N-COUNT: usu sing
2.
If you say that something is a ~ to a person or group of people, you mean that it will make them notice something and start to take action.
The Ambassador said he hoped the statement would serve as a ~ to the government.
N-COUNT: usu sing, oft N to n