Telegraph is a system of sending messages over long distances, either by means of electricity or by radio signals. Telegraph was used more often before the invention of telephones.
VERB
给…发电报;用电报发送(信息)
To telegraph someone means to send them a message by telegraph.
If someone telegraphs something that they are planning or intending to do, they make it obvious, either deliberately or accidentally, that they are going to do it.