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, rhinitis, sinuitis, tarsitis, thecitis, tightass, tinnitis, uvulitis, villitis, vulvitis, zemaitis

9 letters:
adnexitis, aerotitis, anconitis, arteritis, arvanitis, balanitis, barotitis, ceratitis, cheilitis, chorditis, cloacitis, colonitis, conchitis, corneitis, coronitis, cryptitis, decubitis, decubitus, didymitis, eburnitis, enronitis, expeditus, fasciitis, gastritis, glossitis, hepatitis, hepititus, hymenitis, 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, 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, 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, balanoposthitis, blepharadenitis, costochondritis, cystourethritis, dermatomyositis, endomyocarditis, endomyometritis, endophthalmitis, enterogastritis, enterohepatitis, fibrochondritis, keratoscleritis, leptomeningitis, meningomyelitis, nasopharyngitis, neurodermatitis, osteochondritis, pachymeningitis, panencephalitis, parencephalitis, parenchymatitis, pericholangitis, perisalpingitis, perisigmoiditis, photodermatitis, phytodermatitis, pleurohepatitis, radiodermatitis, rhinotracheitis, sclerokeratitis, steatohepatitis, vasovesiculitis

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

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

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

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

20 letters:
encephalomyocarditis, keratoconjunctivitis, phytophotodermatitis

22 letters:
polioencephalomyelitis

24 letters:
laryngotracheobronchitis

4 letters:
ibis

5 letters:
ficus, picus, nidus, midas

7 letters:
azygous, rhibhus

10 letters:
homozygous

11 letters:
chlamydeous

12 letters:
heterozygous, achlamydeous