pouncer

Same as pounce, 2.

In the medieval church in England, a gold or silver thumb-stall placed upon the thumb of a bishop’s right hand after it had been dipped in chrism or holy oil, used out of reverence for the hallowed oils and in order to avoid soiling his vestments until he had washed his hands. Also poncer, ponser, ponsir, thumb-stall.

One who pounces.