单词：nacreous_cloud 

名词

• 
  [1.n.nacreous_cloud] (同义词:[nacreous_cloud]  [mother-of-pearl_cloud]  )
• 
  注释列句：a luminous iridescent cloud at a high altitude that may be seen when the sun is a few degrees below the horizon
• 上位词 -> [cloud( n. 云, 烟云, 天空, 污点 vt. 以云遮敝, 玷污, 使黯然 vi. 乌云密布, 阴沉 )]  [atmospheric_phenomenon]  [physical_phenomenon]  [natural_phenomenon(自然现象 )]  [phenomenon( n. 现象 )]  [process( n. 过程, 作用, 方法, 程序, 步骤, 进行, 推移 vt. 加工, 处理 )]  [physical_entity]  [entity( n. 实体 )]