Can someone me the synonym september 9/11

It was a tragedy for people family members that died

September 11 or 9/11 is a day, should you ask anyone who experienced it that day, will know exactly where they were when it first came over the news. Terrorists killed almost 3,000 people with planes into the two World Trade Center towers (economic centers of USA), the Pentagon (center of our military peer) & would have taken out the White House (center of our government) if it had not been for the courageous actions of the men on board to crash the plane in a field in Pennsylvania.
The day America became forever changed; became highly aware of what hatred can do yet our resolve is to never forget & to always protect our freedoms.
(This is my opinion alone; I am glad this event is being taught in history class)