Ogre, generally
Ogre - as in Shrek
Another word for water that starts with the letter 'O' is oxygen dihydrogen.
originonset
Orator is another word for speaker.
Onus
other
Oh, I'm rich
Orc
oblong.
outstanding i hope this helps B)
oblong; such as an oval or rectangle
Orb, octopus, ow are some examples. you can look in the "o" section in a dictionary for more words.