Interject is now the fancy word for "Silence."
Anything that could be Silenced in 2.0 - 4.5 by Bard or Paladin can now be Interjected instead.
Silence only works on Spells.
Things like Water, Aero, Thunder, etc. And of course, some have much fancier names.

Stun should be saved for stopping physical Abilities like Final Sting etc.