Sunday = η Κυριακή
Monday = η Δευτέρα
Tuesday = η Τρίτη
Wednesday = η Τετάρτη
Thursday = η Πέμπτη
Friday = η Παρασκευή
Saturday = το Σάββατο
The above is nominative case; if you are not aware of cases or Greek, it is too complex really to analyse the correct usage unless you have a specific phrase in mind you want translated.
Abbreviations starting from Sunday.
Κυρ.
Δευτ.
Τρ.
Τετ.
Πέμ.
Παρ.
Σάβ.
Or
["Κυρ.", "Δευτ.", "Τρ.", "Τετ.", "Πέμ.", "Παρ.", "Σάβ."]
Κυρ., Δευτ., Τρ., Τετ., Πέμ., Παρ., Σάβ.
Shorter versions:
["Κ.", "Δ.", "Τρ.", "Τε.", "Πέ.", "Πα.", "Σ."]