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[sem-uh-fawr, -fohr] /ˈsɛm əˌfɔr, -ˌfoʊr/
an apparatus for conveying information by means of visual signals, as a light whose position may be changed.
any of various devices for signaling by changing the position of a light, flag, etc.
a system of signaling, especially a system by which a special flag is held in each hand and various positions of the arms indicate specific letters, numbers, etc.
verb (used with or without object), semaphored, semaphoring.
to signal by semaphore or by some system of flags.
Origin of semaphore
1810-20; < Greek sêma sign + -phore
Related forms
[sem-uh-fawr-ik, -for-] /ˌsɛm əˈfɔr ɪk, -ˈfɒr-/ (Show IPA),
semaphorical, adjective
semaphorically, adverb Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for semaphore
Historical Examples
  • This semaphore arm remained rigid for a second, threatening; then it vibrated with inconceivable rapidity, feinting.

  • "I jess was looking at that thing," she said bashfully, pointing to the semaphore.

  • I listened to the wretched creature Rolland while he told what had happened at the semaphore.

    The Maids of Paradise Robert W. (Robert William) Chambers
  • This invention of Chappe was called the "semaphore Telegraph."

  • A semaphore message was sent to the destroyer next astern to keep a look-out for the drowning man, but he was not seen again.

    A Lively Bit of the Front Percy F. Westerman
  • I knew his praise of my semaphore must be flattery, and yet—I liked it.

    The Abandoned Farmer Sydney Herman Preston
  • The semaphore was nearly a quarter of a mile from the station, and the arm was down.

    A Lover in Homespun F. Clifford Smith
  • Roy did not know whether it had been done by Morse whistling or by semaphore.

    Tom Slade Percy K. Fitzhugh
  • A second method of signaling was by the use of the semaphore.

  • There he set the semaphore to flag the east-bound train from Duluth.

    The Blazed Trail Stewart Edward White
British Dictionary definitions for semaphore


an apparatus for conveying information by means of visual signals, as with movable arms or railway signals, flags, etc
a system of signalling by holding a flag in each hand and moving the arms to designated positions to denote each letter of the alphabet
to signal (information) by means of semaphore
Derived Forms
semaphoric (ˌsɛməˈfɒrɪk), semaphorical, adjective
semaphorically, adverb
Word Origin
C19: via French, from Greek sēma a signal + -phore
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for semaphore

"apparatus for signaling," 1816, probably via French sémaphore, literally "a bearer of signals," ultimately from Greek sema "sign, signal" (see semantic) + phoros "bearer," from pherein "to carry" (see infer). Related: Semaphoric (1808).

Online Etymology Dictionary, © 2010 Douglas Harper
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semaphore in Technology
programming, operating system
The classic method for restricting access to shared resources (e.g. storage) in a multi-processing environment. They were invented by Dijkstra and first used in T.H.E operating system.
A semaphore is a protected variable (or abstract data type) which can only be accessed using the following operations:
P(s) Semaphore s; while (s == 0) ; /* wait until s&gt;0 */ s = s-1;
V(s) Semaphore s; s = s+1;
Init(s, v) Semaphore s; Int v; s = v;
P and V stand for Dutch "Proberen", to test, and "Verhogen", to increment. The value of a semaphore is the number of units of the resource which are free (if there is only one resource a "binary semaphore" with values 0 or 1 is used). The P operation busy-waits (or maybe sleeps) until a resource is available whereupon it immediately claims one. V is the inverse, it simply makes a resource available again after the process has finished using it. Init is only used to initialise the semaphore before any requests are made. The P and V operations must be indivisible, i.e. no other process can access the semaphore during the their execution.
To avoid busy-waiting, a semaphore may have an associated queue of processes (usually a FIFO). If a process does a P on a semaphore which is zero the process is added to the semaphore's queue. When another process increments the semaphore by doing a V and there are tasks on the queue, one is taken off and resumed.
The Free On-line Dictionary of Computing, © Denis Howe 2010
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