rhapsody         
noun [ C ] uk/ˈræp.sə.di/ us/ˈræp.sə.di/
 music specialized狂想曲 
a piece of music that has no formal structure and expresses powerful feelings
  Rachmaninov's "Rhapsody on a Theme of Paganini" 拉赫马尼诺夫的《帕格尼尼主题狂想曲》 
  formal充满激情的演讲(或文章);热情洋溢的发言(或文章) 
a speech or piece of writing that contains powerful feelings and enthusiasm
 Idiom   
go into rhapsodiesidiom  大加赞赏,热情称颂
to express very great enthusiasm and admiration for something
  She went into rhapsodies over/about the chocolate cake. 她对那个巧克力蛋糕赞不绝口。