n. an unknown and unexplored region
n. a variable whose values are solutions of an equation
a. not known
s. not known to exist
a. 不知道的, 未知的, 陌生的
n. 未知物, 未知数
1. The reason for her sudden departure is still unknown.
她突然离开的原因仍然未知。
2. There are many unknown facts about the history of this city.
关于这座城市的历史，还有许多未知的事实。
3. He felt nervous when he faced unknown challenges.
当他面对未知的挑战时感到紧张。