Overheated...
"Obnoxious" and "offensive" are the only ones I can think of.
There are no common synonyms that start with O. Some suggestions:orchidaceous / ostentatious (gaudy, showy)overwhelming / overpowering (irresistable)The word ogleable (watchable, attractive) seems to exist only informally.
Omphalos, but I don't think it has a standard adjectival form.
Some words that start with the letter O are:oceanOddOdeofoffOfficeogreoldOliveOnoneOpalOppositeorOrangeorboreganoorganismorgasmorigamiotherotteroughtOxymoronoval
opinion
Ohio
okra
Ozymandias
Some happy words that start with O include: Overjoyed Optimistic Open-hearted
Synonym=ball o' meat Antonym=cube o' veggies
Some German words that start with the letter O are Opa, Oma and oberflächlich.
ODour