Bent, turned, or thrown back; reflected. Physiology Being an involuntary action or response, such as a sneeze, blink, or hiccup. Produced as an automatic response or reaction: reflex opposition to change. Something, such as light or heat, that is reflected. An image produced by reflection. A copy or reproduction. Physiology An involuntary response to a stimulus. Psychology An unlearned or instinctive response to a stimulus. Linguistics A form or feature that reflects or represents an earlier, often reconstructed, form or feature having undergone phonetic or other change. To bend, turn back, or reflect. To cause to undergo a reflex process.