Any of several small freshwater polyps of the genus Hydra and related genera, having a naked cylindrical body and an oral opening surrounded by tentacles.
A dragon-like creature with many heads and the ability to regrow them when maimed.
A complex, multifarious problem or situation that cannot be solved easily and rapidly.
The presence of a large number of pest organisms in an area or field, on the surface of a host or anything that might contact a host, or in the soil.