Main Entry: 1sem·a·phore
Pronunciation: 'se-m&-"fOr, -"for
Function: noun
Etymology: Greek sEma sign, signal + International Scientific Vocabulary -phore
Date: 1816
1 : an apparatus for visual signaling (as by the position of one or more movable arms)
2 : a system of visual signaling by two flags held one in each hand

for a semaphore illustration you can go to www.m-w.com.