Ovary ?
Outstanding and optimistic are positive words. They begin with the letter o.
Several four letter words begin with the letter q. However, there are no four letter words that begin with the letter q and end with the letter o.
Obedient, obituary, occasion, odorless, offended, offstage, omission and operator are 8 letter words. They begin with the letter o.
Obese and oddball are insulting words. They begin with the letter o.
Openhearted and openminded are the only two I could come up with.openoutstanding
Outgoing, observant, outstanding, orderly and optimistic are positive words that begin with the letter o.
ocean
ornaments
olie
ourselves
On and Of
Orbit and ozone are space words. They begin with the letter o.