WordNet (r) 3.0 (2006):

unembellished
    adj 1: lacking embellishment or ornamentation; "a plain hair
           style"; "unembellished white walls"; "functional
           architecture featuring stark unornamented concrete" [syn:
           plain, bare, spare, unembellished,
           unornamented]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "unembellished":
   arcadian, bald, bare, blank, bucolic, common, commonplace, dull,
   flat, genuine, homespun, humdrum, inartificial, insipid,
   matter-of-fact, mundane, naked, native, natural, naturelike, nude,
   ordinary, pastoral, pedestrian, plain, poetryless, prosaic,
   prosing, prosy, rural, tiresome, unadorned, unadulterated,
   unaffected, unarrayed, unartificial, unassuming, uncomplicated,
   undecked, undecorated, undesigning, undisguising, undissembling,
   undissimulating, undressed, unelaborate, unfeigning, unfurbished,
   ungarnished, unidealistic, unimaginative, unimpassioned,
   unornamented, unostentatious, unpoetic, unpretending,
   unpretentious, unromantic, unsophisticated, unspoiled, untrimmed,
   unvarnished, vapid