mindmap root((罕见)) infrequent implies occurrence at wide intervals in space or time: family visits that were ~ and brief. uncommon suggests something that occurs or is found so infrequently as to be exceptional or extraordinary: smallbox is now ~ in many countries. scarce implies a falling short of a standard or required abundance: jobs were ~ during the Depression. rare suggests extreme scarcity or infrequency and often implies consequent high value: ~ first editions of classics fetch high prices. sporadic implies occurrence in scattered instances or isolated outbreaks: ~ cases of the genetic disorder. (break out突发突然爆发to start suddenly, especially of war, fighting, or similarly undesirable things战争战斗等不良事件突然发生，如a fire/riot/war had broken out突发了火灾/暴乱/战争)