by reasonable definition, 'terrorism' cannot be applied to an act of, or approved by, government The basis for the Afghanistan war was surely that the de facto government of that country backed Al Qaeda in its actions on 911. So according to that "reasonable definition" 911 was not an act of terrorism...

In fact the term "terrorist" actually appears to have been coined to refer specifically to government actions by those in the French government of the time who were responsible for the Reign of Terror. True, the way we use words changes over the years - but the essential element is common to those terrorists and to modern day terrorists - a policy of killing innocent people to achieve a political effect.

If someone explodes a bomb in a railway station in order to kill passengers as a way of affecting public opinion and morale it seems perverse to deny that that is a terrorist act just because the people carrying it out might owe allegiance to some government.