(5S, iOS 7.0.3) App stuck on "Waiting..." on install, but I can launch it from the App Store App.

I was installing Mercury Browser Pro. It seemed like it fully installed but it's simply greyed out and says "Waiting..." on the bottom of its icon. I can't launch it. Tapping it doesn't do anything. Holding it doesn't do anything -- it doesn't give me the option to delete. I connect to iTunes, it's the same...I can delete other apps, but it doesn't give me that option for this one.

Funny thing is, when I launch the App Store app and search for Mercury Browser Pro, it shows up and it gives me an option to "Open." When I click on it, it launches the app fine! So it's stuck in this weird quasi-state that I just can't take the app out from.

Anybody have suggestion on how to recover from this state???

Thanks in advance for any tips.