Ovärderlig, inestimable.
Ovärdig, unworthy.
Oväsen, bustle, stir, noise.
Oväsentlig, unessential, immaterial.
Oxe, ox; oxkött, beef.
Oxstek, roast beef.
Oåterkallelig, irrevocable.
Oåtkomlig, beyond one’s reach, unattainable, inaccessible.
Oädel, ignoble, mean, base.
Oäkta, bastard, not genuine.