n (Greek mythology) monster with nine heads; when struck off each head was replaced by two new ones
n a long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer
n 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
n small tubular solitary freshwater hydrozoan polyp
n an antihypertensive drug (trade name Apresoline) that dilates blood vessels; used (often with a diuretic) to treat hypertension and congestive heart failure