"Complex," "intricate," "complicated," "involved," and "knotty" all mean having confusingly interrelated parts. "Complex" applies to the tangled result of combining a number of things, as in "a complex dance routine." "Intricate" describes an interlacing of parts that makes it nearly impossible to follow them separately, as in "a movie full of intricate plot twists." "Complicated" applies to something that is difficult to understand, solve, or explain, as in "a complicated set of instructions." "Involved" describes extreme complication and often disorder, as in "he gave a rambling, involved explanation." "Knotty" suggests complication and entanglement that make understanding or solving very difficult, as in "a knotty problem."