As Terry Pratchett pointed out in his excellent book *Lords and Ladies*, terms like "great" or "awesome" do not necessarily mean *good*, even though that is how people commonly use them today. One of the most awesome things I have ever seen was a tropical depression making its ponderous way directly towards me when I was camping on an island in the Florida Keys. It was awesome in its terrible power and majesty, and yet most *certainly* not good.

The Wizarding World sees Voldemort similarly to that storm: an unstoppable Juggernaut, great and terrible\* in his malevolence. It is not for no reason that they refuse to say his name. While wizards such as Ollivander may not have necessarily known about things like the horcruxes, they *did* know that any who opposed or disrespected him died. If you saw the Dark Mark hovering over a loved one's home, there could be no doubt as to what had happened.

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\* Interestingly, while Rowling uses the word "great" here in its dated definition of amoral power, she simultaneously uses "terrible" in its modern, morally-connotative use.