Omättlig, insatiable.
Omöjlig, impossible.
Onaturlig, unnatural.
Ond, bad, ill; (vredgad) angry.
Ondska, malice, malignity.
Ondskefull, malicious, malignant.
Onsdag, Wednesday.
Onyttig, useless, fruitless.
Onåd, disgrace, displeasure.
Onämnbar, unmentionable, inexpressible, nameless.