The adjective is a learned borrowing from Latin simplex (“plain, simple; single”).^[1][2] The first part, sim-, comes from Proto-Indo-European *sem-, *sm̥- (“one; together”). The second part, -plex, may be from *pleḱ- (“to weave”).

The noun is derived from the adjective.^[1][3] The plural forms simplices and simplicia are learned borrowings from Latin simplicēs (masculine or feminine) and simplicia (neuter), respectively plural forms of simplex.

Noun sense 1 (“generalization of a triangle or tetrahedron to an arbitrary dimension”) was apparently coined by the Dutch mathematician Pieter Hendrik Schoute (1846–1913) as a short version of Simplicissimum in Mehrdimensionale Geometrie (in German, 1902).^[4] (In his pioneering works on algebraic topology, the French mathematician Henri Poincaré (1854–1912) had previously introduced the concept, but not the actual term simplex.)^[5]

• Adjective and noun (singular form):
  • (Received Pronunciation) IPA^(key): /ˈsɪmplɛks/
  • (General American) IPA^(key): /ˈsɪmˌplɛks/

  • Audio (Southern England):

    (file)

  • Audio (US):

    (file)

  • Hyphenation: sim‧plex
• Noun (plural form: simplices):
  • (Received Pronunciation) IPA^(key): /ˈsɪmplɪsiːz/
  • (General American) IPA^(key): /ˈsɪmpləˌsiz/

  • Audio (US):

    (file)

  • Hyphenation: sim‧pli‧ces
• Noun (plural form: simplicia):
  • (Received Pronunciation, General American) IPA^(key): /sɪmˈplɪsiə/

  • Audio (US):

    (file)

  • Hyphenation: sim‧pli‧cia

simplex (not comparable)

1. (dated) Having a single structure; not composite or complex; undivided, unitary.

   Synonyms: monoplex, uniplex

   Antonym: complex

2. (anatomy, historical) Of an eye: (supposedly) having pigment on only the posterior surface of the iris and not the anterior surface, and thus appearing blue; this was later found to be inaccurate, as eye colour is due to the amount of pigment in the anterior surface of the iris; also, of eye pigmentation: present only on the posterior surface of the iris; and of a person: having eyes with this form of pigmentation.

   Antonym: duplex

3. (computing, telecommunications) Of a circuit or device: involving signals which travel in one direction at a time; unidirectional.

   Antonyms: bidirectional, duplex

   Coordinate terms: full duplex, half-duplex, semiduplex

4. (genetics)
   1. Of a polyploid organism: having one dominant allele at a given locus on all homologous chromosomes.

      Coordinate terms: duplex, nulliplex, triplex

   2. (archaic or obsolete) Synonym of heterozygous (“of an organism: having two different alleles in a given gene”).
5. (linguistics) Of a word: having no (derivational) affixes; simple, monomorphemic, uncompounded.

   Antonym: polymorphemic

6. (originally and chiefly US) Of an apartment (or, sometimes, another type of property): having only one floor or storey; single-storey.

   Coordinate terms: duplex, triplex

• crux simplex
• herpes simplex

simplex (plural simplexes or (algebraic topology, geometry, linguistics) simplices or simplicia)

1. (algebraic topology, geometry) A generalization of a triangle or tetrahedron to an arbitrary dimension, the generalization being the simplest possible convex polytope for a given dimension; more accurately, the convex hull of 👁 {\displaystyle n+1}
   affinely independent points in 👁 {\displaystyle n}
   -dimensional space.
2. (linguistics)
   1. A word which is not compound and contains no derivational affixes (inflectional affixes are usually disregarded); a monomorphemic word.

      The word weak is a simplex. Its derivative weaken is not.

   2. (grammar, archaic) In full simplex sentence: in transformational grammar: a simple sentence which is the product of a few transformations; a kernel sentence.
      • 1978, Helga Harries-Delisle, “Contrastive Emphasis and Cleft Sentences”, in Joseph H[arold] Greenberg, editor, Universals of Human Language, volume 4 (Syntax), Stanford, Calif.: Stanford University Press, →ISBN, page 460:

        The question is: is 139. [“Priexal . ‘arrived Vanya’”] a simplex or is it a cleft structure in which all 'superfluous' constituents were deleted. […] The only indication that 139. is a simplex is the sentence intonation and the absence of a break between the verb and the subject.

        A modified version of a paper published in Working Papers on Language Universals (November 1973), number 12, pages 85–144.

3. (originally and chiefly US) An apartment (or, sometimes, another type of property) having only one floor or storey; a single-storey property.

   Coordinate terms: duplex, triplex

• monoplex

• simplicial
• simplicial complex

• 👁 Image
  simplex on Wikipedia.Wikipedia
• 👁 Image
  simplex (disambiguation) on Wikipedia.Wikipedia

From sem- (“one; single-”) +‎ -plex (“-fold”). The first element (from Proto-Indo-European *sem-, *sm̥-) does not occur independently in Latin, but is also seen in semel (“once”) and semper (“always, forever”). De Vaan reconstructs Proto-Italic *sm̥-plak-s,^[1] but also reconstructs Proto-Italic *-plek-s.^[2]

• (Classical Latin) IPA^(key): [ˈsɪm.pɫɛks]
• (modern Italianate Ecclesiastical) IPA^(key): [ˈsim.pleks]

simplex (genitive simplicis, comparative simplicior, superlative simplicissimus, adverb simpliciter); third-declension one-termination adjective

1. single
2. simple, plain, uncompounded
3. pure, unmixed
4. sincere, naive, frank, open, without guile, guileless, unsuspecting, innocent
   • 8 CE, Ovidius, Fasti 2.225–226:

     male crēditis hostī: simplex nōbilitās, perfida tēla cave!

     You do wrong to trust the enemy: Guileless nobles, beware of treacherous weapons!

5. (mathematics) prime
   • Isidore of Seville, Etymologies 3.5.7:

     Simplices sunt, qui nullam aliam partem habent nisi solam unitatem, ut ternarius solam tertiam, et quinarius solam quintam, et septenarius solam septimam. His enim una pars sola est.

     Prime numbers cannot be partitioned by any other number except one; three has only three, five only five, and seven only seven. For these numbers there is one sole part.

Third-declension one-termination adjective.

• simplicābilis
• simplicitās
• simpliciter

• duplex
• simplus
• triplex
• quadruplex

• “simplex”, in Charlton T. Lewis and Charles Short (1879), A Latin Dictionary, Oxford: Clarendon Press
• “simplex”, in Charlton T. Lewis (1891), An Elementary Latin Dictionary, New York: Harper & Brothers
• "simplex", in Charles du Fresne du Cange, Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
• “simplex”, in Gaffiot, Félix (1934), Dictionnaire illustré latin-français, Hachette.

Borrowed from French simplex.

simplex n (uncountable)

1. simplex