The word juma means "day", so Jumamosi literally means "first day" and Jumapili is "second day".
Saturday and Sunday
Jumamosi na Jumapili
How do you think you would say "Monday"? Recall the Swahili word for three is tatu.
How about "Tuesday" and "Wednesday"?
Tuesday and Wednesday
Juma na Juma
The Swahili language was largely influenced by Arabic and was originally written in Arabic script. The words for "Thursday" and "Friday" are borrowed from Arabic - Alhamisi means "five" in Arabic, and Ijumaa refers to the Muslim day of prayer at the mosque.