Ponder, Pounder, Pender, Pinder, four English surnames with the same meaning. Irish Penders might have a different origin. A pounder, etc., was a sort of law officer who impounded stray cattle, keeping them in a pound. The owner would pay a fine to recover them, and make reparation for any crops, fences or other property damaged. If they couldn't pay I suppose the cattle would be sold off. So our pounder might have had a sideline as a cattle dealer or auctioneer - but that's just speculation.