underbelly

noun

1. The underside of an animal.

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

2. The underside of any thing.

3. figurativelyThe 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.”

4. The soft belly or underside of an animal's bodybody

   Similar: underbody

5. The quality of being weak or unprotected

   “the soft underbelly of the Axis”