n. & v.
n. 1 a a usu. prearranged sign conveying information, guidance, etc. esp. at a distance (waved as a signal to begin). b a message made up of such signs (signals made with flags). 2 an immediate occasion or cause of movement, action, etc. (the uprising was a signal for repression). 3 Electr. a an electrical impulse or impulses or radio waves transmitted as a signal. b a sequence of these. 4 a light, semaphore, etc., on a railway giving instructions or warnings to train-drivers etc. 5 Bridge a prearranged mode of bidding or play to convey information to one's partner.
v. (signalled, signalling; US signaled, signaling) 1 intr. make signals. 2 tr. a (often foll. by to + infin.) make signals to; direct. b transmit (an order, information, etc.) by signal; announce (signalled her agreement; signalled that the town had been taken). signal-book a list of signals arranged for sending esp. naval and military messages. signal-box Brit. a building beside a railway track from which signals are controlled. signal of distress esp. Naut. an appeal for help, esp. from a ship by firing guns. signal-tower US = signal-box. signaller n.
[ ME f. OF f. Rmc & med.L signale neut. of LL signalis f. L signum SIGN ]