Noun
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small tubular solitary freshwater hydrozoan polyp
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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"
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a long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer
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(Greek mythology) monster with nine heads
when struck off each head was replaced by two new ones
"Hydra was slain by Hercules"