den  
noun [ C ] uk/den/ us/den/
  (FOR ANIMALS)     
  (动物的)巢穴,窝
the home of particular types of wild animal
   (ROOM)      
  mainly US活动室,休闲室 
a room in a house or apartment, used for activities not involving work
  The kids are watching TV in the den. 孩子们正在活动室里看电视。 
   (FOR CHILDREN)     
  UK(供孩子玩耍用的)简易房,简易棚 
a rough structure, usually built outside from pieces of wood, cardboard, etc., in which children play
   (CRIME)      
 (从事秘密非法活动的)巢穴,老窝
a place where people secretly plan or take part in dishonest or illegal activities
  a drug/drinking/vice den 毒品/酗酒/犯罪窝点 
often humorous a den of thieves/iniquity 贼窝/魔窟