jawbreaking

adj

1. Very difficult to pronounce.

   “Lord Cockburn, whose forte was not the civil law, affected to listen attentively and take ample notes, when, at last, on Mr Brodie citing some German civilian with a jawbreaking name, his lordship interrupting him asked, […]”

   “If he had, he would probably write and talk in a jawbreaking technical language that we ordinary mortals could not more understand readily than we can work a cross-word puzzle without resorting to the dictionary.”