It could be odd.
Offend is a synonym for the word hurt. It begins with the letter O.
Obliging is a synonym for obedient. It begins with O.
Overwhelming is a synonym for awesome. It begins with O.
Offensive is a synonym for horrible. It begins with the letter O.
on call
synonym for the word horrible that starts with the letter o is offensive, or obnoxious.
on fire; oven-like
Odium is a synonym for hate. It begins with the letter O.
orchestrate is an active word that begins with the letter O
A word meaning to leave out which begins with an "o" is omit.
Opportunity or own decision. Those words mean freedom and begin with O.
it begins with the letter o. but if you are french, it begins with a letter o.