The answer to this clue is a four letter word beginning with O.
The quickest way to get help solving a clue like this - rather than waiting for hours for me to get around to it! - is to use this free online clue solver.
The picture above shows you the answer that resulted when I specified the details you gave me...
This selection comes from an impressive vocabulary program I started playing around with a year or so ago. It's based on a huge dictionary of 150,000 words taken from all the 'big name' vocabulary courses and exams.