This is the 2128th most frequent Polish word.
otwarciu
"Otwarciu" means "opening" (locative or dative case in Polish).
'Otwarciu' is used as a noun in the locative case to describe the time of an event.
Po otwarciu sklepu, klienci zaczęli wchodzić.
After the opening of the store, customers started entering.
Here, 'otwarciu' is a noun in the locative case used to express the topic of discussion.
Rozmawialiśmy o otwarciu muzeum w przyszłym miesiącu.
We talked about the opening of the museum next month.
In this context, 'otwarcia' is the genitive form of the noun, associated with the expression of joy.