Merriam-Webster Collegiate Dictionary - complication

 noun  Date: 15th century  1.  a. complexity, intricacy; especially a situation or a detail of character complicating the main thread of a plot  b. a making difficult, involved, or intricate  c. a complex or intricate feature or element  d. a difficult factor or issue often appearing unexpectedly and changing existing plans, methods, or attitudes  2. a secondary disease or condition developing in the course of a primary disease or condition