One of the mysteries of the English language finally explained.
2Railways. A signal consisting of a pivoted arm that can be in either of two positions, depending on the message to be conveyed. Now chiefly historical, having been largely replaced by electric colour light signals.
3A signal conveyed by or as by semaphore; specifically each of a set of signals that can be represented by the position of a person's two outstretched arms, typically holding a flag in each.
Early 19th century. From semaphore + signal.
semaphore signal/ˈsɛməfɔː ˌsɪɡnl/
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