3 syllables:
consciousness

4 syllables:
class-consciousness, coconsciousness, lose consciousness, preconsciousness, 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:
bottomless, cognizance, columnists, commonness, communists, confidence, conscienceless, consequence, consonance, continence, continents, documents, dominance, godlessness, honestness, modestness, monuments, noxiousness, obstinance, occupants, oculus, ominous, omnibus, omphalus, onymous, opulence, oxalis, pompousness, populace, populous, populus, profitless, prominence, prophetess, protestants, provenance, providence, romulus, rottenness, scolytus, slothfulness, somnolence, spotlessness, squalidness, stolidness, strophanthus, vomitus, watchfulness

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

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

6 syllables:
adrianopolis, bacteriolysis, bacteriophagous, megalobatrachus

7 syllables:
displaying incompetence, genus hippopotamus

8 syllables:
alcoholics anonymous, electronic reconnaissance, urinary incontinence