This is the 788th most frequent Turkish word.
belki
"Maybe" or "perhaps."
Here, 'belki' expresses uncertainty or possibility regarding the weather being nice tomorrow.
Belki yarın hava güzel olur.
Maybe the weather will be nice tomorrow.
'Belki' here conveys a possible plan or consideration for an activity involving going to the cinema with friends.
Belki arkadaşlarımızla sinemaya gidebiliriz.
Perhaps we can go to the cinema with our friends.
In this usage, 'belki' introduces a tentative speculation about someone's statement being truthful, with 'de' adding emphasis.