This is the 948th most frequent Ukrainian word.
перших
"Перших" means "first" (genitive plural form).
The word "перших" is used here as an adjective modifying "гостей" in the masculine genitive plural form, indicating "of the first guests" to show their position or order.
Перших гостей зустріли з великою радістю.
The first guests were met with great joy.
In this sentence, "перших" modifies "днів" in the masculine genitive plural form, describing "the first days" of a specified timeframe.
Ми згадували події перших днів подорожі.
We were recalling the events of the first days of the journey.
Here, "перших" appears in the masculine genitive plural form, describing "the first" in a group, referring to sequence or order.