Mammoth Uncensored Word List:
14 words that are 20 letters long beginning with o in the mammoth uncensored word list.

octogintacentillions octotrigintillionths olivopontocerebellar onychoosteodysplasia otorhinolaryngologic overapprehensiveness overdifferentiations overenthusiastically overintellectualized overintellectualizes overpresumptuousness overprocrastinations overprotectivenesses overrepresentatively