3 syllables:
consciousness

4 syllables:
class-consciousness, coconsciousness, deathconsciousness, lose consciousness, self-consciousness, subconsciousness, unconsciousness

5 syllables:
loss of consciousness, semiconsciousness, stream-of-consciousness, stream of consciousness, unselfconsciousness

15 syllables:
international society for krishna consciousness

3 syllables:
wantonness, concreteness, profitless, populous, ominous, omnibus, concaveness, obtuseness, opulence, providence, cognizance, spotlessness, prominence, oblateness, prophetess, confidence, consonance, commonness, populace, consequence, somnolence, documents, dominance, vomitus, oxalis, bottomless, provenance, populus, polypus, continence, romulus, watchfulness, pompousness, columnists, communists, conscienceless, continents, godlessness, honestness, modestness, monuments, noxiousness, obstinance, occupants, oculus, omphalus, onymous, protestants, rottenness, scolytus, slothfulness, squalidness, stolidness, strophanthus

4 syllables:
predominance, self-confidence, hypostasis, hydrolysis, hypothesis, endogamous, abdominous, metropolis, sarcophagus, synonymous, incontinence, incompetence, concomitance, monogynous, ignobleness, saprophagous, recognizance, obsoleteness, monoclinous, necropolis, anonymous, propositus, passionateness, diplodocus, inconsequence, esophagus, reconnaissance, monotonous, convolvulus, monogamous, homologous, oppositeness, autonomous, incompleteness, apophysis, acropolis, nitrogenous, anthophilous, acrogenous, acromphalus, ammotragus, androgenous, anthophagous, apogamous, apophasis, astomatous, autogenous, autologous, autolysis, carpophagous, cryptogamous, cytolysis, eponymous, exogamous, gymnopilus, hippotragus, idolatress, improvidence, melophagus, obnoxiousness, oesophagus, panonychus, pathologists, phytophagous, psychologists, sarcolemnous, taurotragus, uncommonness, uropsilus, with confidence, zoophagous

5 syllables:
amylolysis, anthropophagus, vote of confidence, electrolysis, entomophilous, opisthognathous, adorableness, megalopolis, hippopotamus, variableness, anemophilous, anisogamous, peloponnesus, acantholysis, air reconnaissance, campylotropous, creeping oxalis, disconsolateness, fibrinolysis, genus oxalis, haematolysis, hematolysis, heterologous, nonautonomous, nonnitrogenous, ophiophagus, proteolysis, stephanopoulos

6 syllables:
adrianopolis, bacteriolysis, bacteriophagous, megalobatrachus

7 syllables:
displaying incompetence, genus hippopotamus

8 syllables:
urinary incontinence, alcoholics anonymous, electronic reconnaissance