This is the 365th most frequent Arabic word.
مهمة
Task, mission, or assignment.
In this context, 'مهمة' refers to a 'mission' or a special job that involves purpose or responsibility.
هي صحفية في مهمة خاصة.
She is a journalist on a special mission.
Here, 'مهمة' (muhimma) is used to mean a 'task' or 'undertaking' that one performs or is assigned.
المهمة كانت صعبة للغاية.
The task was very difficult.
Here, 'مهمة' is used as an adjective meaning 'important,' describing the noun it qualifies.