4 syllables:
indiligence

2 syllables:
vileness

3 syllables:
sisyphus, impetus, sinfulness, impotence, fisticuffs, willingness, blissfulness, childishness, willfulness, imminence, finiteness, synchronous, pythoness, vigilance, innocence, winsomeness, fistulous, minuteness, wickedness, nicholas, ninepence, bibulous, singleness, nimbleness, skittishness, listlessness, synthesis, littleness, insolence, fickleness, silenus, ricinus, syllabus, impishness, litigious, dissonance, dictamnus, indigence, incidence, stimulus, immanence, diclinous, lividness, diffidence, limitless, frivolous, mischievous, singultus, spitefulness, mindlessness, skillfulness, instruments, simpleness, vividness, villainous, alikeness, wistfulness, brittleness, limulus, infamous, tinnitus, chivalrous, citrullus, dissidents, fitfulness, fixedness, gibbousness, givenness, guiltlessness, immigrants, incidents, indolence, innocense, innocents, linanthus, lissomeness, militance, militants, nimravus, quiscalus, risklessness, shiftlessness, siliceous, sinlessness, sinuousness, symptomless, synthesise, thriftlessness, villainess, viscidness, viscousness, wilfulness, windlessness, wishfulness, wrinkleless, cliquishness, fittingness, mytilus, piggishness, priggishness, rypticus, sickeningness, timidness

4 syllables:
coincidence, infiniteness, calyculus, vertiginous, polygamous, indigenous, meticulous, permissiveness, implicitness, distinctiveness, deliciousness, officiousness, ridiculous, religiousness, antithesis, precipitance, restrictiveness, acclivitous, equivalence, saint nicholas, asynchronous, maliciousness, leviticus, duplicitous, capriciousness, significance, cuniculus, precipitous, bicephalous, omnipotence, pediculus, perniciousness, exquisiteness, insipidness, felicitous, explicitness, vindictiveness, ambivalence, acidulous, utriculus, iniquitous, propitiousness, indistinctness, convincingness, suspiciousness, ubiquitous, nonsynchronous, submissiveness, declivitous, definiteness, funiculus, auspiciousness, ambitiousness, ambitionless, antigonus, assiduousness, erithacus, grandiloquence, illicitness, judiciousness, magnificence, magniloquence, munificence, nutritiousness, participants, unchivalrous, unmindfulness, unskillfulness, ventriculus, certificates, commitedness, forgivingness, long-windedness, quick-wittedness, slow-wittedness, tightfistedness, umbilicus

5 syllables:
telekinesis, insignificance, meretriciousness, indefiniteness, acquisitiveness, canaliculus, diakinesis, chemosynthesis, irreligiousness, inauspiciousness, geosynchronous, infelicitous, aspergillosis, unambiguous, biosynthesis, cercopithecus, dryopithecus, expeditiousness, inexplicitness, injudiciousness, kenyapithecus, lufengpithecus, mental synthesis, nonequivalence, repetitiousness, rudapithecus, sivapithecus, unpropitiousness, unpermissiveness

6 syllables:
angle of incidence, australopithecus, conditioned stimulus, aegyptopithecus, algeripithecus, aversive stimulus, negative stimulus, positive stimulus, relative incidence

7 syllables:
ouranopithecus, reinforcing stimulus

8 syllables:
genus australopithecus

10 syllables:
negative reinforcing stimulus, positive reinforcing stimulus