A Welch oath, frequently mentioned in a jocular manner by persons, it is hoped, ignorant of its meaning; which is, By God’s blood, and the nails with which he was nailed to the cross.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Oddfellows * Odd-come-shortlysNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes