5 letters:
-itis, bitis, citas, citis, cytus, ditas, gitis, ictis, litas, mitis, ritus, sitis, situs, titas, titis, titus, vitas, vitis, vitus

6 letters:
clitus, iritis, myitis, otitis, unitas, whitis

7 letters:
actitis, cecitis, cocytus, coxitis, cytitis, fleitas, gonitis, ileitis, ostitis, salitis, samitis, smritis, uveitis, vagitus

8 letters:
adenitis, angiitis, artritis, bolbitis, bulbitis, bursitis, caecitis, corditis, cyclitis, dartitis, dermitis, desmitis, detritus, discitis, diskitis, fascitis, faucitis, hyalitis, lienitis, mammitis, mastitis, mazaitis, mephitis, metritis, moraitis, myelitis, myositis, neuritis, omasitis, ophritis, orchitis, osteitis, pruritis, pyelitis, rachitis, rectitis, sinuitis, tarsitis, thecitis, tightass, tinnitis, uvulitis, villitis, vulvitis, zemaitis

9 letters:
adnexitis, aerotitis, anconitis, arteritis, arthritis, arvanitis, balanitis, barotitis, ceratitis, cheilitis, chorditis, cloacitis, colonitis, conchitis, corneitis, coronitis, cryptitis, decubitis, decubitus, didymitis, eburnitis, enronitis, expeditus, fasciitis, gastritis, glossitis, hepatitis, hepititus, hymenitis, invite us, jejunitis, keratitis, limenitis, lymphitis, mucositis, nephritis, nymphitis, odontitis, omentitis, onychitis, palatitis, panotitis, parotitis, petraitis, phallitis, phlebitis, phrenitis, phyllitis, pleuritis, posthitis, pouchitis, proctitis, rhabditis, rhachitis, scleritis, scrotitis, serositis, sinusitis, sodalitas, steatitis, strumitis, synovitis, tenonitis, tenositis, trachitis, trichitis, typhlitis, vaginitis, zonulitis

10 letters:
abomasitis, alveolitis, amnionitis, aphroditus, bronchitis, capsulitis, cephalitis, cerebritis, cervicitis, chondritis, clientitis, dactylitis, delightous, dermatitis, duodenitis, enthesitis, fibrositis, gangliitis, gaulanitis, gingivitis, heraclitus, laringitis, laryngitis, meibomitis, meningitis, meniscitis, mondayitis, myringitis, neuronitis, omphalitis, oophoritis, orchiditis, panuveitis, petrositis, polyclitus, propositus, pulmonitis, stomatitis, syringitis, tendonitis, tenontitis, tonsilitis, tracheitis, trigonitis, urethritis

11 letters:
adenoiditis, adrenalitis, blepharitis, cholangitis, choroiditis, endangiitis, endaortitis, ependymitis, esophagitis, ethmoiditis, funiculitis, glissonitis, mastoiditis, myocarditis, myofascitis, myometritis, panosteitis, paradenitis, periostitis, peritonitis, phalangitis, pharyngitis, placentitis, polycleitus, pyometritis, pyomyositis, radiculitis, salpingitis, sclerotitis, sigmoiditis, spondylitis, staphylitis, struvite us, syndesmitis, thyroiditis, trachelitis, trachonitis, urarthritis, vaginalitis, vesiculitis

12 letters:
cholangeitis, clitoriditis, deferentitis, descemetitis, diphtheritis, elephantitis, encephalitis, endocystitis, endometritis, epaphroditus, epididymitis, episcleritis, epityphlitis, folliculitis, gonarthritis, hidradenitis, hydradenitis, keratoiritis, lithophytous, lymphangitis, mastadenitis, mononeuritis, oesophagitis, panarthritis, panniculitis, pansinusitis, parametritis, parodontitis, periadenitis, periaortitis, pericystitis, peridesmitis, perimetritis, perineuritis, periosteitis, periovaritis, podarthritis, polyadenitis, polyangiitis, polymyositis, polyneuritis, pyonephritis, rectocolitis, sacroiliitis, sesamoiditis, sialadenitis, vestibulitis

13 letters:
acroarthritis, aerosinusitis, antiarthritis, arachnoiditis, arytenoiditis, barosinusitis, blennadenitis, bronchiolitis, canaliculitis, cholecystitis, dacryadenitis, endophlebitis, epicondylitis, fibromyositis, gastradenitis, gastrocolitis, hemiglossitis, iridocyclitis, jejunoileitis, lymphangeitis, mediastinitis, meibomianitis, mesophlebitis, nasosinusitis, neurodermitis, neuromyositis, osteomyelitis, paranephritis, paraproctitis, parasynovitis, periarthritis, pericolonitis, pericoronitis, perigastritis, perihepatitis, perinephritis, periodontitis, periproctitis, perityphlitis, poliomyelitis, polyarthritis, polyserositis, proctocolitis, pylephlebitis, radioneuritis, scleradenitis, sialoadenitis, sialodochitis, tenosynovitis, tenovaginitis

14 letters:
acrodermatitis, analysis situs, caenorhabditis, cholangiolitis, conjunctivitis, dacryoadenitis, diverticulitis, endocervicitis, hermaphroditus, hyaloserositis, iridokeratitis, lithonephritis, metrophlebitis, mycomyringitis, oligoarthritis, osteoarthritis, osteophlebitis, peribronchitis, pericementitis, perichondritis, perimeningitis, periurethritis, photokeratitis, photoretinitis, pododermatitis, polychondritis, pyelonephritis, pyoperitonitis, pyosalpingitis, rhinosinusitis, tendosynovitis, tendovaginitis, trachelomyitis, vulvovaginitis

15 letters:
acarodermatitis, achillobursitis, acute gastritis, balanoposthitis, blepharadenitis, costochondritis, cystourethritis, delta hepatitis, dermatomyositis, endomyocarditis, endomyometritis, endophthalmitis, enterogastritis, enterohepatitis, fibrochondritis, gouty arthritis, keratoscleritis, leptomeningitis, meningomyelitis, nasopharyngitis, neurodermatitis, osteochondritis, pachymeningitis, panencephalitis, parencephalitis, parenchymatitis, pericholangitis, perisalpingitis, perisigmoiditis, photodermatitis, phytodermatitis, pleurohepatitis, radiodermatitis, rhinotracheitis, sclerokeratitis, serum hepatitis, steatohepatitis, vasovesiculitis, viral hepatitis

16 letters:
actinodermatitis, adenopharyngitis, arthrochondritis, blepharoadenitis, chorioamnionitis, choriomeningitis, gastroduodenitis, iridochoroiditis, metroperitonitis, neurochoroiditis, osteoperiostitis, panbronchiolitis, pelviperitonitis, periencephalitis, perifolliculitis, periophthalmitis, retroperitonitis, rhinopharyngitis, rokas jokubaitis, spondylarthritis, thrombophlebitis

17 letters:
cephalomeningitis, cerebromeningitis, chronic gastritis, encephalomyelitis, erythrodermatitis, gingivostomatitis, laryngotracheitis, leukoencephalitis, orchiepididymitis, pneumoperitonitis, polioencephalitis, proctosigmoiditis, retinochoroiditis, sclerochoroiditis, tracheobronchitis

18 letters:
chronic bronchitis, epididymo-orchitis, glomerulonephritis, laryngopharyngitis, oophorosalpingitis, pharyngolaryngitis, pseudofolliculitis

19 letters:
cystopyelonephritis, encephalomeningitis, epidemic meningitis, meningoencephalitis, prostatovesiculitis, thrombolymphangitis

20 letters:
encephalomyocarditis, infectious hepatitis, keratoconjunctivitis, phytophotodermatitis, rheumatoid arthritis

21 letters:
epidemic encephalitis

22 letters:
degenerative arthritis, lethargic encephalitis, polioencephalomyelitis

23 letters:
hashimoto's thyroiditis

24 letters:
laryngotracheobronchitis

29 letters:
juvenile rheumatoid arthritis

4 letters:
ibis

5 letters:
ficus, picus, midas, nidus

6 letters:
drypis

9 letters:
wood ibis

10 letters:
homozygous, geothlypis

12 letters:
heterozygous