Signal1  —n. 1 a sign (usu. Prearranged) conveying information etc. B message of such signs. 2 immediate cause of action etc. (her death was a signal for hope). 3 a electrical impulse or impulses or radio waves transmitted as a signal. B sequence of these. 4 device on a railway giving instructions or warnings to train-drivers etc. —v. (-ll-; us -l-) 1 make signals. 2 a (often foll. By to + infin.) Make signals to; direct. B transmit or express by signal; announce.  signaller n. [latin: signum sign]