Learner's definition of DEMISE
1 : an end of life : death
She had/owned no property at the time of her demise.
The musician met an untimely demise.
There are several theories about what caused the demise [=extinction] of the dinosaurs.
2 : the end of something that is thought of as being like a death
We have not had truly local news coverage since the town newspaper's demise three years ago.
the company's imminent demise
Losing this game will mean/spell the team's demise.