hotbed

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An environment conducive to vigorous growth or development, especially of something undesirable: a hotbed of intrigue.
2. n. A glass-covered bed of soil heated with fermenting manure or by electricity, used for the germination of seeds or for protecting tender plants.

Century Dictionary and Cyclopedia

1. n. In horticulture, a bed of earth heated by fermenting substances, and covered with glass to defend it from the cold air, intended for raising early plants, or for protecting tender exotics.
2. n. Figuratively, a seat of rapid growth or development, or of eager activity of some kind: generally in a bad sense: as, a hotbed of sedition.
3. n. In rail-making, the bed on which the redhot rail taken from the rolls is placed to cool.

Wiktionary

1. n. 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. A hotbed works as a miniature hothouse, i.e. greenhouse.
2. n. by extension an environment that is ideal for the growth or development of something, especially of something undesirable

GNU Webster's 1913

1. adj. (Iron Manuf.) an iron platform in a rolling mill, on which hot bars, rails, etc., are laid to cool.
2. n. (Gardening) A bed of earth heated by fermenting manure or other substances, and covered with glass, intended for raising early plants, or for nourishing exotics.
3. n. A place which favors rapid growth or development.

WordNet 3.0

1. n. a bed of earth covered with glass and heated by rotting manure to promote the growth of plants
2. n. a situation that is ideal for rapid development (especially of something bad)