A Complication

1. The act or process of complicating.
2. The state of being complicated; intricate or confused relation of parts; complexity.
3. A person who doesn't fit in with the main scheme of things; an interloper.
4. (medicine) A disease or diseases, or adventitious circumstances or conditions, coexistent with and modifying a primary disease, but not necessarily connected with it.
5. (horology) A feature beyond basic time display in a timepiece.