on fire; oven-like
on call
It could be odd.
Obliging is a synonym for obedient. It begins with O.
Overwhelming is a synonym for awesome. It begins with O.
Odium is a synonym for hate. It begins with the letter O.
Offend is a synonym for the word hurt. It begins with the letter O.
Offensive is a synonym for horrible. It begins with the letter O.
Opportunity or own decision. Those words mean freedom and begin with O.
"actual" begins with "a" and is a synonym for "real".
Fossil is a synonym of old and antique and begins with an F.
Adequate is a synonym for Sufficient that begins with a.
synonym for the word horrible that starts with the letter o is offensive, or obnoxious.