3 syllables:
essity, ness city

4 syllables:
necessity

5 syllables:
nonnecessity, of necessity, unnecessity, wenxuecity

9 syllables:
certificate-of-necessity

3 syllables:
wallaby, colony, comradely, hostilely, broccoli, modesty, wannabe, possibly, rocketry, ology, quantity, novelty, policy, bodily, sodomy, botany, psalmody, homily, prodigy, sovereignty, monstrously, boloney, honesty, twopenny, audibly, frostily, honestly, constantly, quality, ptolemy, hostelry, bonhomie, comedy, dobsonfly, solidly, dovekie, commonly, potbelly, potently, romany, polony, constancy, monody, progeny, wantonly, modestly, consciously, gossipy, colloquy, crotchety, prosody, monandry, cobwebby, odyssey, prophecy, contrasty, probably, wobbly, wannabee, polity, oddity, conakry, benghazi, bestially, breathlessly, brevity, centrally, chemically, chemistry, clemency, credibly, density, deputy, desperately, destiny, devilry, dextrously, dreadfully, ebony, ecstasy, ectropy, elegy, embassy, emigree, empathy, endlessly, enemy, enmity, entity, entropy, equity, evilly, fecklessly, federally, felony, flexibly, gemini, generally, heavenly, heavily, helpfully, helplessly, jealously, jealousy, jejunely, kennedy, legacy, legatee, legibly, lemony, lengthily, lenity, leprosy, medically, melanie, melody, mentally, peasantry, pebbly, pedantry, pederasty, pedigree, penally, penalty, pleasantly, pleasantry, preciously, preferably, pregnancy, presently, readily, recipe, remedy, resiny, restfully, revelry, secondly, self-pity, selflessly, senselessly, sensibly, sentiency, separately, sesame, seventy, severally, specially, specialty, splendidly, steadily, stephanie, tenancy, tenantry, tendency, tensity, tentatively, tepidly, testily, threnody, trenchancy, trepidly, velvety, venally, vengefully, weaponry, yemeni, zealotry, zestfully, zestily

4 syllables:
monopsony, ontogeny, monotony, volubly, autonomy, pomology, cacophony, synonymy, astronomy, psephology, technology, sinology, topography, horology, colostomy, conchology, mycology, misogamy, aerology, oncology, demography, geometry, zoology, homogeny, economy, monopoly, ecology, frivolity, garbology, doxology, tocology, neurology, philology, democracy, apostrophe, cytology, lithography, ontology, impolitely, anthology, pornography, comradery, thermometry, geology, geodesy, phonology, phytology, hypocrisy, nosology, demonstrably, orthography, ethnology, penology, gastronomy, misology, typography, ichthyology, agrology, trade policy, improbably, impossibly, apostasy, moronity, comparably, proctology, equality, commodity, despondently, inconstancy, spectroscopy, prodigally, impotency, pathology, philosophy, bureaucracy, planography, dishonesty, photography, theology, neology, virology, conjugally, apology, cartography, unconsciously, ethology, serology, psychology, mammography, ethnography, mahogany, insolvency, allopathy, hydrometry, theocracy, phylogeny, tautology, optometry, morphology, agronomy, otology, astrometry, urology, histology, hydrology, geography, mythology, despondency, chronology, posology, anomaly, biology, responsibly, allometry, biography, dichotomy, phrenology, fluoroscopy, low comedy, holography, astrology, enology, idolatry, spectrometry, homology, monogamy, seismology, autocracy, petrology, limnology, acceptably, acephaly, allegedly, amenity, anemone, ascendancy, ascendency, complexity, confederacy, confessedly, contemptuously, convexity, death penalty, defencelessly, dependency, detestably, discrepancy, domenici, especially, essentially, eventually, exceptionally, expectancy, extremity, fidelity, flux density, forelady, hegemony, heredity, identity, illegibly, immensity, impendency, impetuously, incessancy, incessantly, inclemency, incredibly, indemnity, ineffably, inequity, infectiously, inflexibly, insensibly, integrity, intensity, intrepidly, jack kennedy, lamentably, licentiously, lieutenancy, lobectomy, longevity, low density, lumpectomy, mastectomy, nephrectomy, neurectomy, nonentity, ostensibly, penelope, perceptibly, perplexedly, perplexity, polemically, potentially, pretentiously, professedly, professionally, quiescency, rebelliously, refreshfully, regrettably, relentlessly, repentantly, respectably, respectfully, resplendency, resplendently, revengefully, schenectady, sententiously, sequentially, serenity, shell entity, solemnity, splenectomy, successfully, supremacy, telemetry, telepathy, thrombectomy, transcendency, tremendously, unhelpfully, unpleasantly, unsteadily, vasectomy, vulvectomy, with empathy

5 syllables:
laparoscopy, hematology, macrocephaly, archeology, anemometry, toxicology, aetiology, cardiography, angiology, actinometry, physiology, eschatology, teratology, rheumatology, anthropology, etymology, child psychology, uranology, true anomaly, dermatology, hagiology, volcanology, mineralogy, bibliography, depth psychology, audiometry, lexicography, haematology, ophthalmology, radiology, axiology, fiscal policy, primatology, inequality, scientology, embryology, herpetology, gynaecology, parisology, roentgenography, stereoscopy, etiology, high technology, jejunostomy, crystallography, aristocracy, foreign policy, ideology, egyptology, trigonometry, oenology, mediocrity, teleology, choreography, radiography, methodology, paleology, speleology, ideography, terminology, audiology, genealogy, cardiology, archaeology, sociology, poenology, entomology, immunology, criminology, ornithology, climatology, adenopathy, irresponsibly, oceanography, anemography, hagiography, tracheostomy, lexicology, meniscectomy, sociometry, pharmacology, plane geometry, gerontology, anthropometry, densitometry, anisogamy, gynecology, chromatography, anorthography, angiography, episiotomy, accidentally, acrocephaly, anencephaly, appendectomy, biochemistry, change integrity, change intensity, clinocephaly, coalescency, conscientiously, consequentially, create mentally, deferentially, detrimentally, disrespectfully, drunken revelry, embolectomy, field intensity, fundamentally, geochemistry, half-intensity, high-fidelity, high fidelity, hydrocephaly, hysterectomy, incidentally, independency, independently, intumescency, laminectomy, laryngectomy, life expectancy, line of destiny, mask of pregnancy, mastoidectomy, megacephaly, microcephaly, mortal enemy, mountain ebony, nanocephaly, naval weaponry, oophorectomy, open sesame, orchidectomy, orchiectomy, penitentially, photochemistry, pneumonectomy, prostatectomy, providentially, reprehensibly, reverentially, rhytidectomy, salpingectomy, scaphocephaly, school of dentistry, sentimentally, sigmoidectomy, stapedectomy, sympathectomy, thyroidectomy, tonsillectomy, tubal pregnancy, unacceptably, unforgettably, unintentionally, unpretentiously, unrepentantly, unsuccessfully, vapor density, white supremacy

6 syllables:
neuroanatomy, cardiomyopathy, antimonopoly, token economy, psychopathology, market economy, bacteriology, solid geometry, social democracy, autobiography, social psychology, musical comedy, endocrinology, human ecology, chromolithography, paleobotany, ultrasonography, geomorphology, folk etymology, neuropsychology, meteorology, biotechnology, cinematography, parapsychology, glottochronology, offset lithography, palaeontology, epistemology, arteriography, neurobiology, insurance policy, paleontology, numismatology, applied psychology, telephotography, microbiology, moral philosophy, adenoidectomy, adrenalectomy, anas penelope, appendicectomy, change of integrity, cholecystectomy, coincidentally, cosmetic dentistry, electrochemistry, environmentally, experimentally, genus penelope, immunochemistry, inconsequentially, interdependency, manifest destiny, militant tendency, organic chemistry, ovariectomy, panhysterectomy, pedal extremity, physical chemistry, radiochemistry, relative density, simple mastectomy, unsentimentally

7 syllables:
projective geometry, natural theology, situation comedy, anesthesiology, psychopharmacology, physical geography, radio astronomy, clinical psychology, paper chromatography, spherical geometry, african mahogany, paleopathology, epidemiology, bioclimatology, philippine mahogany, cognitive psychology, paleobiology, social anthropology, psychophysiology, dialect geography, electromyography, column chromatography, paleornithology, natural philosophy, neurophysiology, doctor of philosophy, immunopathology, abdominal pregnancy, department of chemistry, executive clemency, feeling of identity, inorganic chemistry, john fitzgerald kennedy, magnetic flux density, magnetic intensity, ovarian pregnancy, radical mastectomy, suprarenalectomy, total hysterectomy

8 syllables:
cultural anthropology, micropaleontology, congenital anomaly, physical anthropology, comparative psychology, economic geography, paleoclimatology, molecular biology, proprietary colony, hyperbolic geometry, industrial psychology, paleoanthropology, analytic geometry, political economy, conformational entropy, interpersonal chemistry, radical hysterectomy

9 syllables:
developmental psychology, experimental psychology

10 syllables:
physiological psychology, modified radical mastectomy