iceberg

Short definition from Wiktionary

Noun

1. 1
   The seaward end of a glacier.
2. 2
   A huge mass of ocean-floating ice which has broken off a glacier or ice shelf
3. 3
   An aloof person.
4. 4
   An impending disastrous event whose adverse effects are only beginning to show.
5. 5
   A topic that is more convoluted and fractal than it may seem.
6. 6
   A topic that is more convoluted and fractal than it may seem: A list, infographic, or other enumeration of such a topic and its subcomponents, often ordered into groups sorted by obscurity and bizarreness.