Acrimony is bitterness, or ill will. Acrimony is a spiteful word. It sounds bitter, like acid.
Acrimony comes from the Latin word acrimonia, meaning basically "sharpness." Although it sounds like matrimony, the only thing the words have in common is the suffix from monium which means "state, condition." So it's the state of being acrid, or bitter. It's not just for married folks, though — this slightly dusty noun can refer to any sharp, bitter feeling. After a drawn-out court case, there might be lingering acrimony stirred up during the trial. Not surprisingly, it's also the name of a British heavy metal band from the '90s.