hydra

hydra
/ˈhaɪdrə; `haɪdrə/ n
1 (in Greek mythology) snake-like monster with many heads that grew again if they were cut off （希腊神话中的）蛇怪（长著许多头, 斩去後能重新长出）.
2 (fig 比喻) thing that is hard to get rid of; recurring problem 难以除掉的事物; 一再出现的问题.

牛津英汉双解词典