The Collaborative International Dictionary of English v.0.48:

Prosaic \Pro*sa"ic\, Prosaical \Pro*sa"ic*al\, a. [L. prosaius,
   from prosa prose: cf. F,. prosa["i]que. See Prose.]
   1. Of or pertaining to prose; resembling prose; in the form
      of prose; unpoetical; writing or using prose; as, a
      prosaic composition. --Cudworth.
      [1913 Webster]

   2. Dull; uninteresting; commonplace; unimaginative; prosy;
      as, a prosaic person. --Ed. Rev.
      [1913 Webster] -- Pro*sa"ic*al*ly, adv. --
      Pro*sa"ic*al*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

prosaic
    adj 1: not fanciful or imaginative; "local guides describe the
           history of various places in matter-of-fact tones"; "a
           prosaic and unimaginative essay" [syn: matter-of-fact,
           prosaic]
    2: lacking wit or imagination; "a pedestrian movie plot" [syn:
       pedestrian, prosaic, prosy, earthbound]
    3: not challenging; dull and lacking excitement; "an unglamorous
       job greasing engines" [syn: commonplace, humdrum,
       prosaic, unglamorous, unglamourous]

Moby Thesaurus II by Grady Ward, 1.0:

126 Moby Thesaurus words for "prosaic":
   Attic, Spartan, actual, arid, ascetic, austere, bald, banal,
   banausic, bare, barren, bland, boring, breadwinning, businesslike,
   candid, characterless, chaste, classic, classical, cliched,
   commercial, common, commonplace, dead, direct, drab, dry, dull,
   earthbound, everyday, factual, flat, frank, garden, garden-variety,
   hackneyed, ho-hum, homely, homespun, household, humdrum, infecund,
   infertile, insipid, irksome, jejune, lackluster, lean, lifeless,
   literal, lowly, lusterless, materialistic, matter-of-fact,
   mediocre, moneymaking, monotonous, mouldy, mundane, natural, neat,
   nondescript, open, ordinary, overdone, pedestrian, plain,
   plain-speaking, plain-spoken, poetryless, practicable, practical,
   prose, prosing, prosy, pure, pure and simple, realistic, routine,
   run-of-the-mill, rustic, severe, simple, simple-speaking, sober,
   spare, staid, stale, stark, stereotyped, stock, stolid,
   straightforward, stuffy, tedious, threadbare, tired, tiresome,
   trite, unadorned, unaffected, undistinguished, unembellished,
   uneventful, unexceptional, unfanciful, unideal, unidealistic,
   unimaginative, unimpassioned, uninspired, uninteresting,
   uninventive, unnoteworthy, unoriginal, unpoetic, unpoetical,
   unromantic, unromanticized, unvarnished, utilitarian, vapid,
   workaday, workday, working