reflex
n. countablen. a physical reaction that your body does automatically without you thinking about it. For example, you pull your hand away from a hot stove before you even feel the pain.
n. an involuntary and nearly instantaneous movement in response to a stimulus. Often used to describe biological responses mediated by the nervous system.
The doctor tapped my knee to test my reflex.
A goalkeeper needs incredibly fast reflexes to stop a ball traveling at high speed from such a short distance.
While some behaviors are learned through years of repetition, the startle response remains a primitive reflex designed to protect the organism from sudden environmental threats.
Commonly used in the plural ('reflexes') when referring to a person's general ability to react quickly.