Reflex (noun)

1. An automatic and unconscious response to a stimulus.
2. A movement or action that is performed without conscious thought.

Origin:

From reflexus meaning "bend back".

Examples:

1. The doctor tested his reflexes by tapping his knee with a hammer.
2. The baby's reflexes are developing as he grows.
3. The blink reflex is a common reflex in humans.
4. The reflex action of the muscle helped him avoid the falling object.
5. The reflexes of the elderly person were slower than the young person.