reflex

Short definition from Wiktionary

Noun

1. 1
   An automatic response to a simple stimulus which does not require mental processing.
2. 2
   The descendant of an earlier language element, such as a word or phoneme, in a daughter language.
3. 3
   The ancestor word corresponding to a descendant.
4. 4
   The descendant of anything from an earlier time, such as a cultural myth.
5. 5
   A reflection or an image produced by a reflection; the light reflected from an illuminated surface to one in shade.

Adjective

1. 1
   Bent, turned back or reflected.
2. 2
   Produced automatically by a stimulus.
3. 3
   Having greater than 180 degrees but less than 360 degrees.
4. 4
   Illuminated by light reflected from another part of the same picture.

Verb

1. 1
   To bend back or turn back over itself.
2. 2
   To reflect (light, sight, etc.).
3. 3
   To reflect or mirror (an object), to show the image of.
4. 4
   To cast (beams of light) on something.
5. 5
   To respond to a stimulus.