I sought out this site because I need help finding the origins of a word/phrase that my family uses. We are from Southern Maryland, USA. The exclamation in question is 'debygawd.' I do not know how to spell it. I cannot find any version of it on the internet. My mother has provided a sample definition;
Debygawd (pronounced Dee-by-gaud)- word that provides emphasis to any declarative sentence. Usually followed by "captain" but pronounced "cap-en." Used in a sentence - "Debygawd cap-en them crabs is runnin today! Picked up a bushel and a half in the first 30 minutes.'
We are from the Potomac River/Chesapeake Bay area. I would say old maryland families, generally 'waterbillies' use this term. Tangier Island and Smith Island both come to mind as potential originators.