(uncommon) Synonym of telegraphy, any process for transmitting arbitrarily long messages over a long distance using a symbolic code.

(chiefly historical) The electrical device gradually developed in the early 19th century to transmit messages using Morse code; the entire system used to transmit its messages including overhead lines and transoceanic cables.

(video games) A visible or audible cue that indicates to an opponent the action that a character is about to take.

To use a telegraph.

(figurative) To clearly communicate to another nonverbally, whether by gesture, a change in attitude, or any other sign, especially unintentionally.