Not a very common term in today’s language to be sure. But, it is a real word. It was used by US Congressman Davy Crockett (think Alamo), to describe an Eureka moment.
A famous quote of his was:
“We have the right as individuals to give away as much of our own money as we please in charity; but as members of Congress we have no right to appropriate a dollar of the public money.”
The word itself means something that settles a matter, or a final blow a decisive event.
I recommend listening to the full talk by the legendary, folk hero, and US Congressman, available from RealityZone.com.