The Collaborative International Dictionary of English v.0.48:

Rotten \Rot"ten\, a. [Icel. rotinn; akin to Sw. rutten, Dan.
   radden. See Rot.]
   Having rotted; putrid; decayed; as, a rotten apple; rotten
   meat. Hence:
   (a) Offensive to the smell; fetid; disgusting.
       [1913 Webster]

             You common cry of curs! whose breath I hate
             As reek of the rotten fens.          --Shak.
       [1913 Webster]
   (b) Not firm or trusty; unsound; defective; treacherous;
       unsafe; as, a rotten plank, bone, stone. "The deepness of
       the rotten way." --Knolles.
       [1913 Webster]

   Rotten borough. See under Borough.

   Rotten stone (Min.), a soft stone, called also Tripoli
      (from the country from which it was formerly brought),
      used in all sorts of finer grinding and polishing in the
      arts, and for cleaning metallic substances. The name is
      also given to other friable siliceous stones applied to
      like uses.
      [1913 Webster]

   Syn: Putrefied; decayed; carious; defective; unsound;
        corrupt; deceitful; treacherous.
        [1913 Webster] -- Rot"ten*ly, adv. -- Rot"ten*ness,
        n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

rotten
    adj 1: very bad; "a lousy play"; "it's a stinking world" [syn:
           icky, crappy, lousy, rotten, shitty,
           stinking, stinky]
    2: damaged by decay; hence unsound and useless; "rotten floor
       boards"; "rotted beams"; "a decayed foundation" [syn:
       decayed, rotten, rotted]
    3: having decayed or disintegrated; usually implies foulness;
       "dead and rotten in his grave"

Moby Thesaurus II by Grady Ward, 1.0:

289 Moby Thesaurus words for "rotten":
   abandoned, abominable, amiss, amoral, appalling, arrant, atrocious,
   awful, bad, bad-smelling, baneful, barfy, base, beastly,
   beneath contempt, bent, blameworthy, brackish, brutal, bum,
   cankered, carious, cloying, conscienceless, contaminated,
   contemptible, corroded, corrupt, corrupted, crappy, criminal,
   crooked, crumbling, crumbly, dark, debased, debauched, decadent,
   decayed, deceitful, decomposed, decomposing, decrepit, degenerate,
   degraded, deplorable, depraved, despicable, deteriorating,
   detestable, devious, dire, disagreeable, disgusting, dishonest,
   dishonorable, disintegrating, displeasing, dissatisfactory,
   dissolute, doubtful, dreadful, dubious, egregious, enormous,
   evasive, evil, fecal, feculent, felonious, festering, fetid,
   filthy, fishy, flagitious, flagrant, flyblown, foul, fraudulent,
   friable, frowsty, frowy, frowzy, fulsome, funky, fusty, gamy,
   gangrened, gangrenous, gloppy, gone bad, graveolent, grievous,
   grim, gross, gunky, hateful, heinous, hideous, high, horrendous,
   horrible, horrid, horrific, horrifying, icky, ill, ill-got,
   ill-gotten, ill-smelling, immoral, indirect, infamous, infirm,
   iniquitous, insidious, lamentable, loathsome, lousy, low, low-down,
   maggoty, malodorous, mawkish, mean, mephitic, miasmal, miasmic,
   mildewed, mildewy, miserable, moldy, monstrous, morally polluted,
   mortified, mouldy, mucky, musty, nasty, nauseant, nauseated,
   nauseating, nauseous, necrosed, necrotic, nefarious, nidorous,
   noisome, not kosher, notorious, noxious, obnoxious, odious,
   odorous, off, offensive, olid, ordurous, outrageous, overripe,
   peccant, perverse, perverted, pitiable, pitiful, poisonous,
   polluted, poor, poorish, profligate, puky, punk, putrefied,
   putrescent, putrid, questionable, rancid, rank, reasty, reasy,
   rebarbative, reechy, reeking, reeky, regrettable, reprehensible,
   reprobate, repulsive, ropy, rotten at, rotting, rough, sad, scabby,
   scandalous, schlock, scummy, scurfy, scurvy, shabby, shady,
   shameful, shameless, shifty, shitty, shocking, shoddy, sick,
   sickening, sinister, slabby, slimy, slippery, sloppy, sloshy,
   sludgy, slushy, smellful, smelling, smelly, sordid, sour, soured,
   sphacelated, spoiled, spoilt, sposhy, squalid, stale,
   steeped in iniquity, stenchy, stinking, strong, stuffy, sulfurous,
   suppurating, suppurative, suspicious, tainted, terrible, too bad,
   touched, tragic, tricky, turned, ulcerated, unclean, unconscienced,
   unconscientious, unconscionable, underhand, underhanded, unethical,
   unfirm, unhappy, unhealthy, unpleasant, unprincipled,
   unsatisfactory, unsavory, unscrupulous, unsolid, unsound,
   unspeakable, unstable, unstraightforward, unsturdy, unsubstantial,
   unwell, up, venal, vice-corrupted, vile, villainous, vitiated,
   vomity, warped, weevily, wicked, without remorse, without shame,
   woeful, wormy, worst, worthless, wretched, wrong, yecchy, yucky