impotent  
adjective uk/ˈɪm.pə.tənt/ us/ˈɪm.pə.t̬ənt/
  (LACKING POWER)      
  无力量的;无能力的
not having the power or ability to change or improve a situation
  You feel so impotent when your child is ill and you cannot help them. 当孩子生病却什么忙也帮不上时,你会觉得自己是如此无能为力。 
   (SEXUAL PROBLEM)       
 (男子)阳痿的
If a man is impotent, he cannot have sex because his penis cannot become hard or stay hard.
  (男性)不育的
If a man is impotent, he is unable to have children.