oscilar - to oscillate, to fluctuate

oscurecer - to darken

otorgar - to grant

oir - to hear

orientar - to orient

orinar - to urinate, to piss

ostentar - to flaunt, to hold

oxidar - to rust, to oxidize, to oxidate

obscurecerse - to become dim

obstruir - to obstruct

oxear - to shoo

ocluir - occlude

obviar - eliminate, eliminating, get rid of, redressorientarse - orientate

osificarse - ossify

orquestar - orchestrate

oponerse - oppose