O·zark Plateau or O·zark Mountains 
(ōzärk′)
(ōzärk′) An upland region of the south-central United States extending from southwest Missouri across northwest Arkansas into eastern Oklahoma.
- on the rack
- on the rag
- on-the-record
- on the right foot
- on the road
- on the rocks
- on the ropes
- on the run
- on the same wavelength
- on-the-scene
- on the shelf
- on the side
- on the sly
- on the spectrum
- on the spot
- on the square
- on the street
- on the strength of
- on the string
- on the surface
- on the table
- on the take
- on the tapis
- on the tip of (one's) tongue
- on the tip of one's tongue