iceberg

noun

1. (obsolete)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.”

   “Clissold the excellent cook, who should have gone with the motor party, tumbled off a small iceberg and concussed himself while posing or 'ponting' as it had come to be known- Griffith Taylor, with his usual wit, had defined 'to pont' as 'to spend a deuce of a time posing in an uncomfortable position'.”

   “The passengers still on board were keen to watch as Tessa's crew scrambled for their positions, and she heard jokes about icebergs and devil's triangles, and anxious childish queries answered by soothing adult tones.”

3. (US, slang)An aloof person.
4. (figuratively)An impending disastrous event whose adverse effects are only beginning to show.

   “He has little to lose: at present he will go down in history, alongside George W. Bush, as a skipper who ignored the looming fiscal iceberg.”

5. (Internet, figuratively, slang)A topic that is more convoluted and fractal than it may seem.

   “Near-synonym: rabbit hole”

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

   “There's a massive iceberg of increasingly crazy fanfics out there based around those two characters.”

6. (Internet, broadly, figuratively, slang)A topic that is more convoluted and fractal than it may seem.

   “Check out the gaming iceberg on this post! There's some really freaky titles there that I've never heard of.”

   “Today we're gonna talk about the Star Wars iceberg.”