1. (noun) a long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer

• snake

1. (noun) small tubular solitary freshwater hydrozoan polyp

• genus hydra

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

• greek mythology

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

• mythical creature
• mythical monster

2. (noun) trouble that cannot be overcome by a single effort because of its many aspects or its persistent and pervasive quality

• problem
• trouble

3. (noun) small tubular solitary freshwater hydrozoan polyp

• hydroid
• hydrozoan