mercurial  
adjective uk/mɜːˈkjʊə.ri.əl/ us/mɝːˈkjʊr.i.əl/
  (QUICK)         
  literary多变的,反复无常的 
changing suddenly and often
  a mercurial temperament 易变的性情 
 She was entertaining but unpredictable, with mercurial mood swings. 她很会逗人开心,但性格让人捉摸不透,情绪反复无常。 
  literary机智活跃的 
intelligent, enthusiastic, and quick
  a mercurial mind/wit 活跃的思维/机敏的才智 
   (RELATING TO MERCURY)      
 medical specialized含汞的;因汞引起的 
containing or caused by mercury
  mercurial drugs 含汞的药物