omit
A word meaning to leave out which begins with an "o" is omit.
it means something lol
odd
ovine
Outset Origin
One Dutch word beginning with the letter "o" is "onmiddellijk," which means "immediately" in English.
Further Leave to Remain Other
The word is cease.
expelled
oleo
Ovine (refers to sheep).
In Irish names "Mac" means "Son" and "Ó" means "Grandson"