3 syllables:
viciousness, vitiousness

4 syllables:
ambitiousness, auspiciousness, capriciousness, deliciousness, factitiousness, fictitiousness, flagitiousness, judiciousness, lubriciousness, maliciousness, nutritiousness, officiousness, perniciousness, propitiousness, seditiousness, suspiciousness

5 syllables:
adventitiousness, expeditiousness, inauspiciousness, injudiciousness, meretriciousness, repetitiousness, superstitiousness, unambitiousness, unpropitiousness

1 syllable:
jets, sets, metz, bets, sweats, lets, nets, gets

2 syllables:
regrets

3 syllables:
bibulous, blissfulness, brittleness, chivalrous, citrullus, dictamnus, diffidence, diligence, dissidents, dissonance, fickleness, fistulous, fitfulness, fixedness, frivolous, gibbousness, givenness, guiltlessness, immanence, immigrants, imminence, impetus, impotence, incidence, incidents, indolence, infamous, innocence, innocense, innocents, insolence, instruments, limitless, limulus, linanthus, lissomeness, listlessness, littleness, militance, militants, minuteness, mischievous, nicholas, nimbleness, nimravus, quiscalus, risklessness, shiftlessness, siliceous, simpleness, sinfulness, singleness, singultus, sinlessness, sinuousness, skillfulness, stimulus, syllabus, symptomless, synchronous, synthesis, synthesise, thriftlessness, tinnitus, vigilance, villainess, villainous, viscidness, viscousness, vividness, wickedness, wilfulness, willfulness, windlessness, winsomeness, wishfulness, wistfulness, wrinkleless

4 syllables:
acclivitous, acidulous, ambitionless, ambivalence, antigonus, antithesis, assiduousness, asynchronous, declivitous, equivalence, erithacus, explicitness, felicitous, grandiloquence, illicitness, implicitness, indigenous, insipidness, leviticus, magnificence, magniloquence, meticulous, munificence, nonsynchronous, omnipotence, participants, polygamous, religiousness, ridiculous, saint nicholas, unchivalrous, unmindfulness, unskillfulness, utriculus, ventriculus

5 syllables:
biosynthesis, cercopithecus, chemosynthesis, dryopithecus, geosynchronous, inexplicitness, infelicitous, irreligiousness, kenyapithecus, lufengpithecus, mental synthesis, nonequivalence, rudapithecus, sivapithecus, unambiguous

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

7 syllables:
ouranopithecus, reinforcing stimulus

8 syllables:
genus australopithecus

10 syllables:
negative reinforcing stimulus, positive reinforcing stimulus