swear on (one's) mother's grave

(redirected from sworn on someone's mother's grave)

swear on (one's) mother's grave

To make a very serious, solemn pledge, especially that one is telling the truth. Janet has sworn on her mother's grave that she wasn't the one to betray me, and I believe her. I swear on my mother's grave that if I have a chance to help your campaign, I will.
See also: grave, on, swear