Possible Clues:

• It's de rigueur for a diplomat
• Diplomat-ic skill
• Bumpkin's lack
• Careful wording, maybe
• 'The art of making guests feel at home when that's really where you wish they were'
• Race embraces account of diplomacy
• Way with words from the first part of play
• In this one would be wholly diplomatic
• What churls lack
• Sign of refinement