re·flex 
(rēflĕks′)
(rēflĕks′)adj.
1. Physiology Being an involuntary action or response, such as a sneeze, blink, or hiccup.
2. Produced as an automatic response or reaction: reflex opposition to change.
3. Bent, turned, or thrown back; reflected.
4. Reflexed.
n.
1.
a. Physiology An involuntary response to a stimulus.
b. reflexes A person's ability to respond to new or changing stimuli: His quick reflexes make him a good taxi driver.
2. Psychology An unlearned or instinctive response to a stimulus.
3. Linguistics A form or feature that reflects or represents an earlier, often reconstructed, form or feature having undergone phonetic or other change.
4.
a. Something, such as light or heat, that is reflected.
b. An image produced by reflection.
c. A copy or reproduction.
[From Middle English reflexen, to refract light, bend back, from Latin reflexus, past participle of reflectere, to bend back; see REFLECT.]