Nonentity
A person of thing or little importance
Non sequitur
Something that doesn’t logically follow
Obdurate
Stubborn, hard hearted
Obfuscate
To confuse; to bewilder
Obloquy
Strong disapproval; a bad reputation resulting from public
Obsequious
Excessively submissive or overly attentive
Obviate
To prevent; to get around
Onerous
Burdensome; heavy; hard to endure
Onus
A burden, responsibility, obligation
Nirvana
A place of great peace or happiness.