This is the 17574th most frequent Russian word.
трудной
"Трудной" means "difficult" or "hard."
Here, 'трудной' is used as a feminine adjective in the instrumental case, describing the characteristic of the noun 'задача' (task).
Задача оказалась трудной.
The task turned out to be difficult.
In this case, 'трудной' is again an adjective modifying 'ситуацией' (situation), with the noun in the instrumental case due to the preposition 'с' (with).
Она столкнулась с трудной ситуацией.
She faced a difficult situation.
Here, 'трудной' describes 'вопрос' (question), with the sentence showcasing its usage as a descriptive adjective implying complexity or challenge.