Den and Hotbed

Den noun - The shelter or resting place of a wild animal.

Hotbed and den are semantically related in haunt topic. In some cases you can use "Hotbed" instead a noun "Den", when it comes to topics like cavern.

Hotbed noun - A place or environment that favors the development of something.

Den and hotbed are semantically related in breeding ground topic. You can use "Den" instead a noun "Hotbed".