quill·back 
(kwĭlbăk′)
(kwĭlbăk′)n. pl. quillback or quill·backs
A North American freshwater fish (Carpiodes cyprinus) that has one ray of the dorsal fin extending conspicuously beyond the others.
- 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
- on the tip of tongue
- on the town
- on the up and up
- on the up-and-up and up
- on the up-and-up/up and up
- on the upgrade
- on the wagon