exceptionalism. noun. 1  the condition of being exceptional. 2  an exceptional or unique nature ascribed to a nation, culture, etc. and regarded as giving it a special role in history, world affairs, etc.3  the belief in this.xceptionalism. noun. 1  the condition of being exceptional. 2  an exceptional or unique nature ascribed to a nation, culture, etc. and regarded as giving it a special role in history, world affairs, etc. 3  the belief in this.