Hydra

1. Greek Mythology. The many-headed monster that was slain by Hercules.
2. A constellation in the equatorial region of the southern sky near Cancer, Libra, and Centaurus. Also called Snake.
3. A persistent or multifaceted problem that cannot be eradicated by a single effort.

[Middle English Idra, from Latin Hydra, from Greek Hudrā, Hydra, a water serpent.]

The noun has 2 meanings:

Meaning #1: (Greek mythology) monster with nine heads; when struck off each head was replaced by two new ones

Meaning #2: a long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer
  Synonym: Snake