The Collaborative International Dictionary of English v.0.48:

Deformity \De*form"i*ty\, n.; pl. Deformities. [L. deformitas,
   fr. deformis: cf. OF. deformet['e], deformit['e], F.
   difformit['e]. See Deform, v. & a., and cf. Disformity.]
   1. The state of being deformed; want of proper form or
      symmetry; any unnatural form or shape; distortion;
      irregularity of shape or features; ugliness.
      [1913 Webster]

            To make an envious mountain on my back,
            Where sits deformity to mock my body. --Shak.
      [1913 Webster]

   2. Anything that destroys beauty, grace, or propriety;
      irregularity; absurdity; gross deviation from order or the
      established laws of propriety; as, deformity in an
      edifice; deformity of character.
      [1913 Webster]

            Confounded, that her Maker's eyes
            Should look so near upon her foul deformities.
                                                  --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

deformity
    n 1: an affliction in which some part of the body is misshapen
         or malformed [syn: deformity, malformation,
         misshapenness]
    2: an appearance that has been spoiled or is misshapen; "there
       were distinguishing disfigurements on the suspect's back";
       "suffering from facial disfiguration" [syn: disfigurement,
       disfiguration, deformity]

Moby Thesaurus II by Grady Ward, 1.0:

205 Moby Thesaurus words for "deformity":
   aberration, abnormality, absurdity, acute disease, affection,
   affliction, ailment, allergic disease, allergy, amputee, anticness,
   atrophy, awfulness, bacterial disease, birth defect, birthmark,
   bizarreness, bizarrerie, blackhead, bleb, blemish, blight, blister,
   bowlegs, bulla, camelback, cardiovascular disease, check,
   chronic disease, cicatrix, circulatory disease, cleft palate,
   clubfoot, comedo, complaint, complication, condition,
   congenital defect, crack, crater, craze, cripple, crookback,
   curiousness, damage, defacement, defect, defective,
   deficiency disease, deformation, degenerative disease, disability,
   disease, disfiguration, disfigurement, disorder, distemper,
   distortion, dreadfulness, endemic, endemic disease,
   endocrine disease, epidemic disease, fantasticality, fault,
   flatfoot, flaw, forbiddingness, freakishness, freckle,
   frightfulness, functional disease, fungus disease,
   gastrointestinal disease, genetic disease, ghastliness, grisliness,
   grotesqueness, grotesquerie, gruesomeness, handicap,
   handicapped person, harelip, hemangioma, hereditary disease,
   hickey, hideousness, horribleness, horridness, humpback, hunchback,
   iatrogenic disease, idiot, illness, imbecile, impairment,
   incapable, indisposition, infectious disease, infirmity, injury,
   irregularity, keloid, kink, knock-knee, kyphosis, lentigo,
   loathsomeness, lordosis, malady, malaise, malconformation,
   malformation, milium, misproportion, misshape, misshapenness, mole,
   monstrosity, monstrousness, morbidity, morbus, muscular disease,
   mutilation, needle scar, neurological disease, nevus,
   nutritional disease, occupational disease, oddity, offensiveness,
   organic disease, outlandishness, pandemic disease, paralytic,
   paraplegic, pathological condition, pathology, peculiarity, pimple,
   pit, plant disease, pock, pockmark, port-wine mark,
   port-wine stain, protozoan disease, psychosomatic disease, pustule,
   quadriplegic, quaintness, queerness, repugnantness, repulsiveness,
   respiratory disease, rift, rockiness, scab, scar, scratch,
   sebaceous cyst, secondary disease, seediness, sickishness,
   sickness, signs, singularity, splayfoot, split, strangeness,
   strawberry mark, sty, swayback, symptomatology, symptomology,
   symptoms, syndrome, talipes, teratism, teratology, terribleness,
   the crippled, the handicapped, the pip, torticollis, track,
   truncation, twist, unnaturalness, urogenital disease, valgus,
   verruca, vesicle, virus disease, wale, warp, wart, wasting disease,
   weal, weirdness, welt, wen, whitehead, worm disease, wryneck