imponderable /ɪmˈpɒndərəbəl/

• 1. 

  N-COUNT An imponderable is something unknown and difficult or impossible to estimate or make correct guesses about. 难以估算的; 难以猜透的; 无法估量之事

  例：

  They are speculating on the imponderables of the future.

  他们猜测着未来难以估算的事情。