arbitration: (law) the hearing and determination of a dispute by an impartial referee agreed to by both parties (often used to settle disputes between labor and management)
discussion: an exchange of views on some topic
plaster of paris: any of several gypsum cements; a white powder (a form of calcium sulphate) that forms a paste when mixed with water and hardens into a solid; used in making molds and sculptures and casts for broken limbs