This is the 677th most frequent Ukrainian word.
певні
"Певні" means "certain" or "sure" in English.
Here, 'певну' implies certainty or clarity, modifying 'впевненість' (confidence).
Ми маємо певну впевненість у його словах.
We have certain confidence in his words.
In this sentence, 'певні' indicates a specific subset of people, translated as 'Certain'.
Певні студенти вже склали цей іспит.
Certain students have already passed this exam.
The word 'певний' conveys assurance or confidence about a fact, used adjectivally here.