1a: Reflected heat, light, or color; b: a mirrored image.
2a: An automatic and often inborn response to a stimulus that involves a nerve impulse passing inward from a receptor to the spinal cord and thence outward to an effector (as a muscle or gland) without reaching the level of consciousness and often without passing to the brain (the knee-jerk reflex); b: the process that culminates in a reflex and comprises reception, transmission, and reaction; c: reflexes plural: the power of acting or responding with adequate speed.