This is the 597th most frequent Greek word.
κυριακής
"Κυριακής" means "of Sunday" or "Sunday's" in English.
"Κυριακές" is used here to denote specific days of the week, in a plural form.
Η αγορά είναι κλειστή τις Κυριακές.
The market is closed on Sundays.
"Κυριακή" refers to a specific day associated with an event, Easter Sunday in this case.
Πήγαμε στη θεία μας για Κυριακή του Πάσχα.
We went to our aunt's house for Easter Sunday.
"κυριακής" is used as an adjective to describe the garden, associating it with Sunday.