over and under
odalisque
oriole
Otto comes to mind.
orlop
osier
Obediah?!
Orc, Olog-hai
A few examples of 3-letter words starting with the letter O are:owloweoaroatown
Some six letter words starting with O are:objectoblongoccultocelotoddityoffendofficeorangeorioleorphanoverdooxygen
Old Navy and OshKosh B'Gosh are clothing brands. They begin with the letter O.
insects starting with letters O X and Z