This is the 1049th most frequent Japanese word.
困難
Difficulty; hardship.
Used as a noun describing the difficulty of succeeding in an endeavor.
そのプロジェクトを成功させることは、困難でした。
Achieving success in that project was challenging.
Used as an adjective modifying a noun to describe the challenging nature of the situation.
困難な状況でも、私はあきらめませんでした。
Even in a difficult situation, I did not give up.
Used as a noun referring to obstacles or challenges that were overcome.