As far as I know omnibar relates either to the Safari Omnibar or to the Google Chrome omnibar / omnibox.
As for the Safari Omnibar, it's basically a tweaked location bar (
"Search directly using location bar"), and location-bar is a synonym of address-bar.
As for the Google omnibar / omnibox, even Google calls it "address bar" so no need to refer to it as "omnibar".
22 out of the 23 questions tagged with omnibar relate to the Google Chrome address bar, and only 1 relates to the Safari one.
Can omnibar be merged into address-bar and be a tag synonym of address-bar?