anything that serves to indicate, warn, direct, command, or the like, as a light, a gesture, an act, etc.

a traffic signal; a signal to leave.

anything agreed upon or understood as the occasion for concerted action.

an act, event, or the like that causes or incites some action

The unjust execution was the signal for revolt.

a token; indication.

Electronics . an electrical quantity or effect, as current, voltage, or electromagnetic waves, that can be varied in such a way as to convey information.

Cards . a play that reveals to one's partner a wish that he or she continue or discontinue the suit led.

serving as a signal; used in signaling

a signal flag.

unusual; notable; outstanding

a signal exploit.

to make a signal to.

to communicate or make known by a signal.

to make communication by a signal or signals.

adjective

insignificant , unexceptional , unimpressive , unnoteworthy

adjective

arresting , arrestive , characteristic , conspicuous , distinctive , distinguished , eminent , exceptional , eye-catching , famous , illustrious , individual , marked , memorable , momentous , notable , noteworthy , noticeable , peculiar , prominent , pronounced , remarkable , renowned , salient , significant , striking , bold , observable , outstanding , pointed

noun

alarm , alert , beacon , bleep , blinker , cue , flag , flare , gesture , go-ahead * , green light * , high sign * , indicator , mark , mayday , movement , nod , okay * , omen , sign , sos , tocsin , token , wink , gesticulation , indication , motion

verb

beckon , communicate , flag , flash , gesticulate , gesture , motion , nod , semaphore , sign , signalize , warn , wave , wink , alarm , arrow , blinker , buzzer , command , cress , cue , extraordinary , flare , horn , image , impulse , indicator , lantern , memorable , message , notable , noticeable , notify , outstanding , password , presage , prominent , remarkable , signify , siren , sound , tocsin , toot , warning , whistle