reflex noun

ADJ. good, lightning, quick | poor | automatic | natural | conditioned

VERB + REFLEX trigger The rapid movement of an object towards the eye triggers the blink reflex. | control | sharpen, speed up The training is designed to sharpen the fighter's reflexes. | slow (down) Alcohol can slow your reflexes. | suppress | test The doctor tested her reflexes.

REFLEX + NOUN action, reaction Almost as a reflex action, I grab my pen as the phone rings.

PREP. by ~ Almost by reflex, he helped himself to a drink.