swearengen: v, tr.
1. To declare or affirm solemnly by invoking a deity or a sacred person or thing.
2. To utter or bind oneself to (an oath).
3. To say or affirm earnestly and with great conviction.
A friend left me with a heavy secret the other day and sealed the deal by looking me in the eye and saying “swearengen.”
In HBO’s Deadwood, The Old West pinkie swear is a spit shake. Mr. Wu and Dan, Al’s flunkie, seal deals with Swearengen slick-palmed, so we did too, with an oath of “swearengen” in Wu’s Chinese accent.