formidable/ˈfɔːmɪdəb(ə)l/
adj.1. 可怕的；令人生畏的a person with a formidable appearance面目可憎的人
The head of the research section was a formidable old professor.研究室主任是个令人望而生畏的老教授。
2. 艰难的；难以克服的a formidable question难以回答的问题
They faced formidable difficulties in their attempt to reach the mountain summit.他们在试图登上山顶时遇到了难以克服的困难。