Semaphore: A signaling system. A semaphore uses flags, lights, or mechanical arms to send messages, usually to travelers. You might see a semaphore next to the railroad tracks.
The word might also refer to a system of sending messages by holding the arms or flags in certain positions. The positions indicate an alphabetic code.
English snagged this word from the French in 1816. If this ticked the French off, they could not say anything. After all, they themselves had snagged the roots from the Greeks. Σῆμα (sêma) means, sign, and φέρω (phérō) means, I carry.