semaphore
/ˈseməfɔ:(r); `sɛməˌfɔr/ n
1 [U]
system of sending signals by holding the arms or two flags in certain positions to indicate letters of the alphabet 旗语
send a message by semaphore 用旗语发送信息.
2 [C] device with red and green lights on mechanically moved arms, used for signalling on railways （铁路的）臂板信号机. semaphore, v [I, Tn, Tf, Dpr.f, Dpr.w, Dpr.t nopassive 不用於被动语态]
send (messages) by semaphore 用旗语发送（信息）
semaphore (to sb) that help is needed/to send help （向某人）打旗语求救.