oversimplification vs. simplism
otherworldliness vs. spirituality
obsoleteness vs. superannuation
obsequiousness vs. subservience
orthogonality vs. perpendicularity
oligodendria vs. oligodendroglia
overestimation vs. overvaluation
overestimate vs. overvaluation
overappraisal vs. overvaluation
overestimation vs. overreckoning
overestimate vs. overestimation
otorhinolaryngology vs. rhinolaryngology