This is the 2464th most frequent Arabic word.
مجهولة
"مجهولة" means "unknown" or "unspecified."
In this sentence, 'مجهول' (majhool) is used as an adjective meaning 'unknown', describing the source of the letter.
تلقى خطابًا من مصدر مجهول.
He received a letter from an unknown source.
Here, 'المجهولة' (al-majhoola) is used as an adjective in the plural form with a definite article to mean 'the unknown things'.
الشعور بالخوف يأتي من الأشياء المجهولة.
Fear arises from unknown things.
Here, 'مجهولة' (majhoola) is used as an adjective meaning 'unknown' describing places.