ob, op in the way, against object – to be against something; obscure – hard to understand; opposition – the act of resistance or action against.

oct/a/o eight octagon – a figure with 8 sides and 8 angles; octogenarian – person in his or her 80s; octopus – sea animal with 8 arms.

ocu eye binoculars – lens device for seeing distances; monocula – relating to one eye; oculist – an eye doctor.

omni all omnipotent – with all the power; omniscient – knowing all things; omnivorous eating all foods.

op/t/s eye, visual condition, sight optic – relating to the eyes; optician – a person who fits eyeglasses; autopsy – the examination of a dead body.

opt best optimal – the best, the most desirable; optimize – to make the best of; optimum – the best something could be.

ortho straight orthodontist – a dentist that straightens teeth; orthopedic – a doctor concerned with the proper alignment of the bones; orthography – the correct way of writing.

osteo bone osteoarthritis – inflammation caused by degeneration of the joints; osteopathy – therapy that uses among others manipulation of the skeleton to restore health; osteology – the study of bones.

out goes beyond, surpasses, exceeds Outgoing – being of lively, sharing nature; outdoing – doing better than; outdoor – outside.

over excessive overconfident – more confident than is appropriate; overstock – more supplies than is desirable; overexcited – ,more excited than one should be.

oxy sharp oxymoron – combining two ideas that sharply contradict each other; oxydize – corrode a surface.