semaphorenoun/ˈsɛm.əˌfɔː/

• 1

  Any equipment used for visual signalling by means of flags, lights, or mechanically moving arms, which are used to represent letters of the alphabet, or words.

  • We must here take the liberty of expostulating with Sir Home [Riggs] Popham and the first Lord of the Admiralty, for having given to the telegraphic machine, invented by that gallant officer, the barbarous name of Semaphore, instead of Sematophore or Semophore—either of them ugly enough.
  • The large Silver Medal of the Society was this Session voted to Nic[h]olas Harris Nicolas, Esq. of the Inner Temple, for an Improvement on the Vertical Semaphore, and for his method of adapting a shifting Key to Telegraphic Communications, for the purpose of insuring their Secrecy. A Model of Mr. N's Semaphore has been placed in the Repository of the Society.
• 2

  A visual system for transmitting information using the above equipment; especially, by means of two flags held one in each hand, using an alphabetic and numeric code based on the position of the signaller's arms; flag semaphore.

  • Its [the article's] object is to furnish a rule for determining the number of distinct signals which can be made by any semaphore, whatever be the number of arms or indicators, of whatever be the number of positions of each arm. In the Cyclopædia of Rees, the number of signals which the semaphores of the line of communication between Paris and Landau were capable of making, is stated to be 823,543, which is no less than 1,274,608 fewer than the real number, an error not arising from the press, but from the principle of computation.
  • 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 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

  computingengineeringmathematicsA bit, token, fragment of code, or some other mechanism which is used to restrict access to a shared function or device to a single process at a time, or to synchronize and coordinate events in different processes.

  • The thread increments the semaphore to prevent other threads from entering the critical section at the same time.
  • Several synchronization techniques have been proposed and many of them have been adopted by parallel and distributed operating systems or parallel programming platforms. [...] Semaphores represent another synchronization technique that is mainly used by traditional stand-alone operating systems.

semaphoreverb/ˈsɛm.əˌfɔː/

• 1

  To signal using, or as if using, a semaphore, with the implication that it is done nonverbally.

  • The person intending to Semaphore will make the International Code Signal VOX (I am going to Semaphore to you), and set his Semaphore at the alphabetical sign [...] with the Indicator out, and wait until the person to whom the Semaphore signal is to be made hoists his answering pennant close up. [...] The British method of Semaphoring by flags held in the hand which is shown in plate VIII is exactly the same as the British Movable Semaphore system, which has just been explained, the positions of the apparatus which denote the letters, numbers, and special signs being, it will be seen, identical in each case, and the only difference being in the apparatus employed.
  • 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.