This is the 6245th most frequent Russian word.
уверенную
"Confident" (feminine accusative singular form).
'уверенной' describes the intonation, showing it has a quality of confidence.
Она говорит с уверенной интонацией.
She speaks with a confident intonation.
Here, 'уверенную' is used as an adjective describing the type of attempt made, emphasizing confidence.
Анна сделала уверенную попытку решить задачу.
Anna made a confident attempt to solve the problem.
In this example, 'уверенную' modifies 'команду', indicating that the team should possess confidence.