A terrorist is "a person who uses unlawful violence and intimidation, especially against civilians, in the pursuit of political aims." As to be unlawful they are by definition non-state actors, no state -- or even a disputed state -- can be a terrorist. The newly-edited omission in the definition is that terrorist wish to force social and political changes through the creation of fear. That is, if we laugh at their insignificance and ignore them, they have no power, whereas a real army has a power beyond fear. The Church's aim in the Inquisition was not that of a powerless and illegal actor inspiring fear as their only goal, but a legal and state-supported power center that was enforcing existing laws, however disagreeable or overzealous. Therefore, no, by any definition, the Church was not a terrorist at that time. I really wish people would stop using the word for any existing violence and aggression, when really they mean "Felon", "combatant", "rebel" or the otherwise correct and accurate term. Labelling people carelessly and inaccurately, and without due process is exactly the objection we have of the Inquisition, so let's not share in their fault.