hydra

(Greek mythology) monster with nine heads; when struck off each head was replaced by two new ones; "Hydra was slain by Hercules"

a long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer

trouble that cannot be overcome by a single effort because of its many aspects or its persistent and pervasive quality; "we may be facing a hydra that defies any easy solution"

small tubular solitary freshwater hydrozoan polyp