Sunday is called as youmul ahad, and monday is youmul ithnain... The rest of the days in a week except Friday are called with their number... But what is the reason only Friday is called jumua?.
1 Answer
The linguistic meaning of "jumuah" is from the root word "jama3ah" (jeem, ayn, meem) which means to gather together. Yawm al-Jumu'ah is thus dubbed because the Muslims gather together for salaat al-jumu'ah (Friday prayers) in congregation -- this is not something you can do individually, but must be done in a group.
Speaking of day names, Saturday is "Yawm As-Sabt" and also does not follow the numbering convention.