offence
Another word for in front is, obverse.
another word for chasm that begins with o omission opening oversight
Oasis
originonset
obi
order
You might be thinking of the word 'omit' or 'omitted'.
One "wow"word (or phrase) beginning with O is "Oh my goodness!" Another = "Oh Wow!"
The word you are looking for is probably - legerdemain. Another synonym for sleight of hand is - Prestidigitation.
Ostrich!
sandcastle
Occult