| noxious | Harmful, poisonous, or very unpleasant | |
| nuance | A subtle difference in or shade of meaning, expression, or sound | |
| obdurate | Stubbornly refusing to change one's opinion or course of action | |
| obfuscated | To make something unclear or obscure, so that it is difficult to understand | |
| objectionable | Arousing disapproval; likely to cause offense or disapproval. | |
| objective | A goal or target that is aimed for | |
| obloquy | Strong public criticism or verbal abuse | |
| obsequious | Excessively obedient or attentive to an ingratiating or servile degree | |
| obstreperous | Noisy and difficult to control | |
| obtrusive | Noticeable or prominent in an unwelcome or intrusive way | |