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.

Common Names:

Name	Pronounced	Usage
Rolo	RAHL-o	English (Rare)
Lidochka	-	Russian
Flora	FLAWR-ə (English), FLO-rah (German)	English, German, Italian, Roman Mythology
Alicia	a-LEE-thya (Spanish), a-LEE-sya (Latin American Spanish), ə-LIS-yə (English), ə-LIS-ee-ə (English), ə-LISH-ə (English), ə-LEE-shə (English)	Spanish, English
Rowell	['rauəl]
Antony	AN-tə-nee	English