From , past participle of reflectere ("to bend back"), equivalent to re- + flex.

• (noun) IPA: /ˈɹiːflɛks/
• (verb) IPA: /ɹɪˈflɛks/

reflex (plural reflexes)

1. An automatic response to a simple stimulus which does not require mental processing.
   • 1970, Stanisław Lem, trans. Joanna Kilmartin and Steve Cox, Solaris (novel):

     For a while, I shall have to make a conscious effort to smile, nod, stand and perform the thousands of little gestures which constitute life on Earth, and then those gestures will become reflexes again.

2. (linguistics) The descendant of an earlier language element, such as a word or phoneme, in a daughter language.

   Synonyms: derivative#Noun

   Antonyms: etymon

   Coordinate term: cognate

3. (linguistics, rare) The ancestor word corresponding to a descendant.
4. The descendant of anything from an earlier time, such as a cultural myth.
   • 1898, Christian Brinton, The Century:

     The superstition of the loup-garou, or werewolf, belongs to the folklore of most modern nations, and has its reflex in the story of "Little Red Riding-hood" and others.

5. (mostly, photography) Reflection or an image produced by reflection. The light reflected from an illuminated surface to one in shade.

   A reflex camera uses a mirror to reflect the image onto a ground-glass viewfinder.

   • c. 1591–1595 (date written), William Shakespeare, “The Tragedie of Romeo and Ivliet”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC ↗, [Act III, scene v]:

     Yon gray is not the morning’s eye,
     ’Tis but the pale reflex of Cynthia's brow.

   • 1850, [Alfred, Lord Tennyson], In Memoriam, London: Edward Moxon, […], →OCLC ↗, (please specify |part=Prologue or Rpilogue, or |canto=I to CXXIX):

     On the depths of death there swims
     The reflex of a human face.

• French: réflexe
• German: Reflex
• Italian: riflesso
• Portuguese: reflexo
• Russian: рефле́кс
• Spanish: reflejo

• French: continuateur
• German: Kontinuante, Fortsetzer
• Italian: riflesso, continuatore
• Spanish: reflejo, continuador

reflex

1. Bent, turned back or reflected.
   • a. 1677 (date written), Matthew Hale, The Primitive Origination of Mankind, Considered and Examined According to the Light of Nature, London: […] William Godbid, for William Shrowsbery, […], published 1677, →OCLC ↗:

     the reflex act of the soul, or the turning of the intellectual eye inward upon its own actions

2. Produced automatically by a stimulus.
3. (geometry, of an angle) Having greater than 180 degrees but less than 360 degrees.
   • 1895, David Eugen Smith, Wooster Woodruff Bernan, New Plane and Solid Geometry, page 7:

     An angle less than a right angle is said to be acute; one greater than a right angle but less than a straight angle is said to be obtuse; one greater than a straight angle but less than a perigon is said to be reflex or convex.

   • 1958, Howard Fehr, “On Teaching Dihedral Angle and Steradian” in The Mathematics Teacher, v 51, National Council of Teachers of Mathematics, page 275:

     If the reflex region is the interior of the angle, the dihedral angle is reflex.

   • 2001, Esther M. Arkin et al., “On the Reflexivity of Point Sets”, in Algorithms and data structures: 7th International Workshop, WADS 2001: Proceedings, Springer, page 195:

     We say that an angle is convex if it is not reflex.

   • 2004, Ana Paula Tomás and António Leslie Bajuelos, “Quadratic-Time Linear-Space Algorithms Generating Orthogonal Polygons with a Given Number of Vertices”, in Computational Science and Its Applications – ICCSA 2004 Proceedings, part 3, Springer, page 117:

     P denotes a polygon and r the number of reflex vertices.

4. (painting) Illuminated by light reflected from another part of the same picture.

• (of an angle) re-entrant

reflex (reflexes, present participle reflexing; simple past and past participle reflexed)

1. (transitive) To bend back or turn back over itself.
2. (transitive, obsolete) To reflect (light, sight, etc.).
3. (transitive, obsolete) To reflect or mirror (an object), to show the image of.
4. (transitive, obsolete) To cast (beams of light) on something.
   • c. 1587–1588, [Christopher Marlowe], Tamburlaine the Great. […] The First Part […], 2nd edition, part 1, London: […] [R. Robinson for] Richard Iones, […], published 1592, →OCLC ↗; reprinted as Tamburlaine the Great (A Scolar Press Facsimile), Menston, Yorkshire, London: Scolar Press, 1973, →ISBN, Act III, scene i ↗:

     The ſpring is hindered by your ſmoothering hoſt,
     For neither rain can fall vpon the earth,
     Nor Sun reflexe his vertuous beames thereon.
     The ground is mantled with ſuch multitudes.

5. To respond to a stimulus.