The Collaborative International Dictionary of English v.0.48:

Simple \Sim"ple\, a. [Compar. Simpler; superl. Simplest.]
   [F., fr. L. simplus, or simplex, gen. simplicis. The first
   part of the Latin words is probably akin to E. same, and the
   sense, one, one and the same; cf. L. semel once, singuli one
   to each, single. Cg. Single, a., Same, a., and for the
   last part of the word cf. Double, Complex.]
   1. Single; not complex; not infolded or entangled;
      uncombined; not compounded; not blended with something
      else; not complicated; as, a simple substance; a simple
      idea; a simple sound; a simple machine; a simple problem;
      simple tasks.
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   2. Plain; unadorned; as, simple dress. "Simple truth."
      --Spenser. "His simple story." --Burns.
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   3. Mere; not other than; being only.
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            A medicine . . . whose simple touch
            Is powerful to araise King Pepin.     --Shak.
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   4. Not given to artifice, stratagem, or duplicity;
      undesigning; sincere; true.
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            Full many fine men go upon my score, as simple as I
            stand here, and I trust them.         --Marston.
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            Must thou trust Tradition's simple tongue? --Byron.
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            To be simple is to be great.          --Emerson.
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   5. Artless in manner; unaffected; unconstrained; natural;
      inartificial;; straightforward.
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            In simple manners all the secret lies. --Young.
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   6. Direct; clear; intelligible; not abstruse or enigmatical;
      as, a simple statement; simple language.
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   7. Weak in intellect; not wise or sagacious; of but moderate
      understanding or attainments; hence, foolish; silly. "You
      have simple wits." --Shak.
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            The simple believeth every word; but the prudent man
            looketh well to his going.            --Prov. xiv.
                                                  15.
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   8. Not luxurious; without much variety; plain; as, a simple
      diet; a simple way of living.
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            Thy simple fare and all thy plain delights.
                                                  --Cowper.
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   9. Humble; lowly; undistinguished.
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            A simple husbandman in garments gray. --Spenser.
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            Clergy and laity, male and female, gentle and simple
            made the fuel of the same fire.       --Fuller.
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   10. (BOt.) Without subdivisions; entire; as, a simple stem; a
       simple leaf.
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   11. (Chem.) Not capable of being decomposed into anything
       more simple or ultimate by any means at present known;
       elementary; thus, atoms are regarded as simple bodies.
       Cf. Ultimate, a.
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   Note: A simple body is one that has not as yet been
         decomposed. There are indications that many of our
         simple elements are still compound bodies, though their
         actual decomposition into anything simpler may never be
         accomplished.
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   12. (Min.) Homogenous.
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   13. (Zool.) Consisting of a single individual or zooid; as, a
       simple ascidian; -- opposed to compound.
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   Simple contract (Law), any contract, whether verbal or
      written, which is not of record or under seal. --J. W.
      Smith. --Chitty.

   Simple equation (Alg.), an equation containing but one
      unknown quantity, and that quantity only in the first
      degree.

   Simple eye (Zool.), an eye having a single lens; -- opposed
      to compound eye.

   Simple interest. See under Interest.

   Simple larceny. (Law) See under Larceny.

   Simple obligation (Rom. Law), an obligation which does not
      depend for its execution upon any event provided for by
      the parties, or is not to become void on the happening of
      any such event. --Burrill.
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   Syn: Single; uncompounded; unmingled; unmixed; mere;
        uncombined; elementary; plain; artless; sincere;
        harmless; undesigning; frank; open; unaffected;
        inartificial; unadorned; credulous; silly; foolish;
        shallow; unwise.

   Usage: Simple, Silly. One who is simple is sincere,
          unaffected, and inexperienced in duplicity, -- hence
          liable to be duped. A silly person is one who is
          ignorant or weak and also self-confident; hence, one
          who shows in speech and act a lack of good sense.
          Simplicity is incompatible with duplicity, artfulness,
          or vanity, while silliness is consistent with all
          three. Simplicity denotes lack of knowledge or of
          guile; silliness denotes want of judgment or right
          purpose, a defect of character as well as of
          education.
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                I am a simple woman, much too weak
                To oppose your cunning.           --Shak.
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                He is the companion of the silliest people in
                their most silly pleasure; he is ready for every
                impertinent entertainment and diversion. --Law.
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