• (RP) IPA: /ˈsɛməfɔː/
• (GA) IPA: /ˈsɛməˌfɔɹ/

semaphore

1. Any equipment use#Verb|used for visual#Adjective|visual signalling#Noun|signalling by means of flag#Noun|flags, light#Noun|lights, or mechanically moving#Adjective|moving arm#Noun|arms which are used to represent letter#Noun|letters of the alphabet, or word#Noun|words.
   • 1875, Marcus Clarke, “Running the Gauntlet”, in His Natural Life [For the Term of His Natural Life], volume III, London: Richard Bentley and Son, OCLC 154638042 ↗, page 27 ↗:

     The arms of the semaphore at the settlement were, in fact, gesticulating with comical vehemence.

   • 1895 January–June, Rudyard Kipling, “An Unqualified Pilot”, in Land & Sea Tales for Scouts and Guides, Bombay: The Gresham Publishing Company; London: Macmillan and Co., published August 1919, OCLC 776877487 ↗, page 68 ↗:

     And so they went down, Jim steering by his father, turn for turn, over the Mayapur Bar, with the semaphores on each bank duly signalling the depth of water, [...]

2. (also, figuratively) A visual system for transmitting information using the above equipment; or (by extension) by means of two flags held one in each hand#Noun|hand, using an alphabetic and numeric code#Noun|code base#Verb|based on the position#Noun|position of the signaller's arms; flag semaphore.
   • 1924 September, Arthur Conan Doyle, “Sidelights on Sherlock Holmes”, in Memories and Adventures, Boston, Mass.: Little, Brown, and Company, OCLC 1367896 ↗, page 110 ↗:

     Buried treasures are naturally among the problems which have come to Mr. [Sherlock] Holmes. One genuine case was accompanied by a diagram here reproduced. [...] Each Indiaman#English|Indiaman in those days had its own semaphore code, and it is conjectured that the three marks upon the left are signals from a three-armed semaphore.

3. (computing) A bit#Noun|bit, token, fragment#Noun|fragment of code, or some other mechanism which is used to restrict access#Noun|access to a shared#Adjective|shared function#Noun|function or device to a single#Adjective|single process#Noun|process at a time#Noun|time, or to synchronize and coordinate#Verb|coordinate events in different processes.

   The thread increments the semaphore to prevent other threads from entering the critical section at the same time.

• Italian: semaforo
• Russian: семафо́р
• Spanish: semáforo

• Italian: semaforo marittimo

• French: sémaphore
• German: Semaphor

semaphore (semaphores, present participle semaphoring; past and past participle semaphored)

1. (ambitransitive, also, figuratively) To signal#Verb|signal use#Verb|using, or as if using, a semaphore, with the implication that it is done non-verbally.
   • 1920 September, Jack London, chapter X, in Hearts of Three, New York, N.Y.: The Macmillan Company, OCLC 1421939 ↗, page 137 ↗:

     These gunny-sack chaps are not animals or savages. Look, Henry! They are semaphoring! See that tree there, and that big one across the cañon. Watch the branches wave.

• Spanish: semáforo