This is the 3055th most frequent French word.
mystérieux
"Mystérieux" means "mysterious" in English.
Describes an attribute of the castle as being intriguing and unexplained.
Le château est mystérieux et plein de légendes.
The castle is mysterious and full of legends.
Qualifies the stranger as unknown and enigmatic.
Un étranger mystérieux est apparu au village hier soir.
A mysterious stranger appeared in the village last night.
References the behavior as being puzzling and not straightforward.