详细解释:n. 水螅, 九头蛇, 难以根除之祸害
词型变化：
名词复数:hydras英语解释：
名词 hydra:
(Greek mythology) monster with nine heads; when struck off each head was replaced by two new onesa long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer同义词：Snake