This is the 18th most frequent Russian word.
уже
"Уже" means "already" or "anymore."
Here, "уже" is used to convey the meaning of 'already,' indicating that an action has been completed earlier than might be expected.
Я уже закончил домашнее задание.
I have already finished my homework.
In this sentence, "уже" emphasizes that a state or condition (darkness) has been reached and it might have occurred quicker or earlier than anticipated.
На улице уже темно.
It is already dark outside.
"Уже" here highlights that a transformation or event has occurred and focuses attention on its occurrence before the expected or discussed moment.