Definition from Wiktionary, the free dictionary
From French télégraphe.
- (historical) An apparatus, or a process, for communicating rapidly between distant points, especially by means of established visible or audible signals representing words or ideas, or by means of words and signs, transmitted by electrical means.
apparatus for communicating between distant points
Derived terms 
- To send a message by telegraph
- To give nonverbal signals to another, as with gestures or a change in attitude.
- Her frown telegraphed her displeasure.
- To show one's intended action unintentionally.