The Collaborative International Dictionary
Corporal oath
Corporal \Cor"po*ral\ (k[^o]r"p[-o]*ral), ||Corporale \Cor`po*ra"le\ (-r?"l?), n. [LL. corporale: cf. F. corporal. See Corporal,a.] A fine linen cloth, on which the sacred elements are consecrated in the eucharist, or with which they are covered; a communion cloth.
Corporal oath, a solemn oath; -- so called from the fact that it was the ancient usage for the party taking it to touch the corporal, or cloth that covered the consecrated elements.
Usage examples of "corporal oath".
But, for my part, that's no business of mine: I must own, if I was put to my corporal oath, I believe she is little better than one of us.