hotbed

hot +‎ bed

hotbed (plural hotbeds)

1. A low bed of earth covered with glass, and heated with rotting manure, used for the germination of seeds and the growth of tender plants, like a miniature hothouse.
2. (by extension) An environment that is ideal for the growth or development of something, especially of something undesirable.
3. An iron platform in a rolling mill, on which hot bars, rails, etc., are laid to cool.

• breeding-ground
• nidus