underbelly

noun

Etymology: From under- + belly.

1. The underside of an animal.

   “We identified the species of the snake by its blue-grey underbelly.”

   “The soft underbelly of the dragon. In the legend, the dragon's armor doesn't cover its stomach.”

2. The underside of any thing.

   “A jolt told me that the Nautilus had bumped the underbelly of the Ice Bank, still quite thick to judge from the hollowness of the accompanying noise.”

3. The side which is not normally seen, normally a dark, immoral place.

   “The area by the canal is the underbelly of town – not something you’d see in the guidebooks.”

   “In order to take the initiative, military leaders from Great Britain and the United States decided to attack in Africa, cross the Mediterranean, and move up against the "soft underbelly" of German-dominated Europe.”