a.

1. 复杂的；难懂的；结构复杂的
   a complicated machine

   结构复杂的机器

   That puzzle is too complicated for the children.

   那个谜语对儿童来说太难了。

adj.

1. consisting of many interconnecting parts; intricate.
   ▸involving many different and confusing aspects.
2. Medicine  involving complications.