The days of the week in Greek are as follows:
All days are feminine except Saturday which is neutral.
Generally in Greek we use the article when referring to the day so Monday is usually written as Η Δευτέρα whereas Saturday is written as Το Σάββατο.
There is also a word for the weekend which is a combination of the words for Saturday and Sunday:
Once you have mastered the days of the week why not try to learn the Greek Months of the Year?