- on the nod
- on the nose
- On the occasion of
- on the off chance
- on the offensive
- on the one hand, on the other hand
- on the one hand on the other hand
- on the open market
- on the order of
- on the other hand
- on the outs
- on the outside
- on the outskirts of
- on the panel
- on the park
- on the part of someone
- on the path/road to self-destruction
- on the path to self destruction
- on the payroll
- on the phone
- on the pill
- on the piss
- on the plus side
- on the point of
- On the positive side