The Collaborative International Dictionary of English v.0.48:

Artless \Art"less\, a.
   1. Wanting art, knowledge, or skill; ignorant; unskillful.
      [1913 Webster]

            Artless of stars and of the moving sand. --Dryden.
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   2. Contrived without skill or art; inartistic. [R.]
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            Artless and massy pillars.            --T. Warton.
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   3. Free from guile, art, craft, or stratagem; characterized
      by simplicity and sincerity; sincere; guileless;
      ingenuous; honest; as, an artless mind; an artless tale.
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            They were plain, artless men, without the least
            appearance of enthusiasm or credulity about them.
                                                  --Porteus.
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            O, how unlike the complex works of man,
            Heaven's easy, artless, unencumbered plan! --Cowper.
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   Syn: Simple; unaffected; sincere; undesigning; guileless;
        unsophisticated; open; frank; candid.
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WordNet (r) 3.0 (2006):

artless
    adj 1: characterized by an inability to mask your feelings; not
           devious; "an ingenuous admission of responsibility" [syn:
           ingenuous, artless] [ant: artful, disingenuous]
    2: simple and natural; without cunning or deceit; "an artless
       manner"; "artless elegance" [ant: artful]
    3: showing lack of art; "an artless translation"
    4: (of persons) lacking art or knowledge [syn: artless,
       uncultivated, uncultured]