This is the 156th most frequent Ukrainian word.
цієї
"Цієї" means "of this" or "this" (genitive or locative feminine singular).
Here, 'цієї' is a demonstrative pronoun in the genitive case singular, modifying the feminine noun 'неділі', specifying 'this Sunday'.
Ми зустрілися вранці цієї неділі.
We met on the morning of this Sunday.
In this sentence, 'цієї' functions as a demonstrative pronoun in the genitive singular for the feminine noun 'події', referring to 'this event'.
Я пам'ятаю яскраві моменти цієї події.
I remember the bright moments of this event.
Here, 'цієї' is used as a genitive singular demonstrative pronoun for the feminine noun 'авторки', focusing on 'this author'.