Mammoth Uncensored Word List:
35 - 19 letter words starting with o

objectionablenesses octogintacentillion octotrigintillionth octovigintillionths osteochondromatosis otorhinolaryngology overambitiousnesses overcapitalizations overcentralizations overclassifications overcommercializing overdifferentiation overdiversification overgeneralizations overidentifications overimaginativeness overindustrialising overindustrializing overintellectualize overintensification overinterpretations overpresumptiveness overprocrastinating overprocrastination overproportionately overrationalization overrepresentations oversensitivenesses oversimplifications overspecializations overspeculativeness oversuperstitiously oversusceptibleness ovolactovegetarians ovoviviparousnesses