obdurate	adjective	stubbornly persistent in wrongdoing; hardened in feelings
obloquy	noun	a strongly condemnatory utterance; abusive language
obstreperous	adjective	marked by unruly or aggressive noisiness; clamorous
obtrusive	adjective	projecting prominent undesirably noticeable
obtuse	adjective	lacking sharpness or quickness of sensibility or intellect; insensitive, stupid; difficult to comprehend; not clear or precise in thought or expression
obviate	verb	to anticipate and prevent (as a situation) or make unnecessary (as an action)
occluded	verb	obstructed; closed off
odious	adjective	arousing or deserving hatred or repugnance; hateful
offal	noun	the waste or by-product of a process: as; trimmings of a hide; the by-products of milling used especially for stock feeds; the viscera and trimmings of a butchered animal removed in dressing; variety meat
officious	adjective	volunteering one's services where they are neither asked nor needed; meddlesome
ominous	adjective	threatening
onerous	adjective	involving, imposing, or constituting a burden; troublesome
opprobrious	adjective	showing scorn or reproach
ossify	verb	to change into bone
ostentation	noun	excessive display; pretentiousness
ostracism	noun	shut out from society refuse to meet talk
overweening	adjective	arrogant, presumptuous