Obdurate
Stubborn and insensitive
Obfuscate
To confuse
Oblique
Indirect
Oblivion
The state of being forgotten
Obscure
Hard to understand
Obsequious
Fawning
Obtuse
Insensitive
Officious
Annoyingly eager to help or advice
Onerous
Burdensome
Opaque
Impossible to see through
Opulent
luxurious
Orthodox
Conventional
Ostensible
Apparent(but misleading)
Ostentatious
Showing off