E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Strike a Bargain (To).
In Latin, fdus ferre; in Greek, horkia temein. The allusion is to the Greek and Roman custom of making sacrifice in concluding an agreement or bargain. After calling the gods to witness, they strucki.e. slewthe victim which was offered in sacrifice. The modern English custom is simply to strike or shake hands.