The Collaborative International Dictionary of English v.0.48:

Bunion \Bun"ion\, n. (Med.)
   Same as Bunyon.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bunyon \Bun"yon\, Bunion \Bun"ion\, n. [Cf. Prov. E. bunny a
   small swelling, fr. OF. bugne, It. bugna, bugnone. See
   Bun.] (Med.)
   An enlargement and inflammation of a small membranous sac
   (one of the burs[ae] muscos[ae]), usually occurring on the
   first joint of the great toe.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bunion
    n 1: a painful swelling of the bursa of the first joint of the
         big toe

Moby Thesaurus II by Grady Ward, 1.0:

207 Moby Thesaurus words for "bunion":
   abscess, adenoiditis, adrenitis, aposteme, appendicitis, arteritis,
   arthritis deformans, arthritis fungosa, arthritis pauperum,
   atrophic arthritis, atrophic inflammation, bed sore, blain, bleb,
   blennorrhagic arthritis, blister, boil, brain fever, bronchitis,
   bubo, bulla, bump, bursitis, canker, canker sore, capillaritis,
   carbuncle, carditis, catarrh, catarrhal inflammation, cerebellitis,
   cerebral meningitis, cerebritis, cerebrospinal meningitis, chancre,
   chancroid, chilblain, chronic infectious arthritis,
   chronic inflammation, cirrhotic inflammation, climactic arthritis,
   clitoritis, cold sore, colitis, collagen disease, conjunctivitis,
   corn, cyst, cystitis, degenerative arthritis, diffuse inflammation,
   dilatation, dilation, distension, edema, encephalitis,
   endocarditis, enteritis, equine encephalomyelitis, eschar,
   exudative inflammation, felon, fester, festering, fever blister,
   fibroid inflammation, fistula, focal inflammation, furuncle,
   furunculus, gastritis, gathering, gingivitis, glossitis,
   gonococcal arthritis, gonorrheal arthritis, gonorrheal rheumatism,
   gout, gouty arthritis, gumboil, hemophilic arthritis, hemorrhoids,
   hepatitis, hyperplastic inflammation, hypertrophic arthritis,
   hypertrophic inflammation, infectional arthritis,
   infectious hepatitis, inflammation, intumescence,
   irritable bowel syndrome, kibe, laryngitis, lesion, lumbago,
   lumbar rheumatism, lump, mastoiditis, meningitis,
   menopausal arthritis, metastatic inflammation, metritis, milk leg,
   mucous colitis, mumps meningitis, myelitis, necrotic inflammation,
   nephritis, neuritis, obliterative inflammation, ophthalitis,
   ophthalmia, orchitis, osseous rheumatism, osteitis, osteoarthritis,
   osteomyelitis, otitis, ovaritis, papula, papule,
   paradental pyorrhea, paronychia, parulis, penitis, pericarditis,
   periodontitis, peritonitis, petechia, pharyngitis, phlebitis,
   piles, pimple, pock, podagra, polyp, proliferative arthritis,
   prostatitis, pustule, pyonephritis, pyorrhea, pyorrhea alveolaris,
   reactive inflammation, rheumatism, rheumatiz, rheumatoid arthritis,
   rhinitis, rising, scab, sclerosing inflammation, sebaceous cyst,
   seroplastic inflammation, serous inflammation, serum hepatitis,
   simple inflammation, sinusitis, soft chancre, sore, spastic colon,
   specific inflammation, stigma, sty, subacute rheumatism,
   suppuration, suppurative arthritis, suppurative inflammation,
   swell, swelling, swollenness, syphilitic arthritis, tennis elbow,
   testitis, thrombophlebitis, tonsilitis, torticollis,
   toxic inflammation, traumatic inflammation, tubercle,
   tuberculous arthritis, tuberculous rheumatism, tumefaction,
   tumescence, tumidity, tumor, turgescence, turgescency, turgidity,
   ulcer, ulceration, ulcerative colitis, uratic arthritis,
   ureteritis, urethral arthritis, urethritis, uteritis, vaginitis,
   vertebral arthritis, visceral rheumatism, vulvitis, wale, welt,
   wen, wheal, whelk, whitlow, wound, wryneck