Noun
(automotive) A blinking light on a motor vehicle that indicates the direction in which it is about to turn.
Synonyms: (informal) blinker, directional, directional signal, direction indicator, (Britain, Australia, New Zealand) indicator, turn indicator, (chiefly US) turn signal
(historical) A semaphore device with a steady light that served the same purpose on early vehicles.
Source: en.wiktionary.org