ˈhīdrə noun
Etymology: alteration (influenced by Latin Hydra ) of earlier idre complicated evil thing, from Middle English Ydre, Ydra Hydra (mythical many-headed serpent slain by Hercules that grew two heads in place of each one that was cut off unless the wound was cauterized), from Middle French & Latin; Middle French Ydre Hydra, from Latin Hydra, from Greek; akin to Greek hydros water snake — more at otter
1. -s : a many-sided problem or obstacle that presents new difficulties each time one aspect of it is solved or overcome
2.
[New Latin, from Latin Hydra (mythical serpent)]
a. -s : any of a number of small freshwater hydrozoan polyps constituting Hydra and related genera, usually living attached to sticks, leaves, or other submerged objects, and consisting of a simple tube with a mouth at one extremity surrounded by a circle of tentacles with which to capture food, the young developing either from eggs or as buds that become detached from the side of the parent after differentiating
b. capitalized : a common genus of hydras