Iceberg

Noun

1. The seaward end of a glacier.
2. A huge mass of ocean-floating ice which has broken off a glacier or ice shelf

   "The Titanic hit an iceberg and sank."

3. An aloof person.
4. An impending disastrous event whose adverse effects are only beginning to show.
5. A topic that is more convoluted and fractal than it may seem.

   "Do some digging into that politician's past life and associates, and you'll see that the iceberg runs deep."