This is the 1437th most frequent Polish word.
zacznie
"Zacznie" means "will start" in English.
In this sentence, 'zacznie' ("will start") functions as the third-person singular future tense form of the verb 'zacząć,' indicating the beginning of an action, specifically rain starting.
Jutro zacznie padać deszcz.
Tomorrow, it will start raining.
Here, 'zacznie' signifies the initiation of thoughtful consideration by a third party, emphasizing the potential change in behavior.
Mam nadzieję, że on zacznie myśleć o innych.
I hope he will start thinking about others.
In this example, 'zacznie się' is a reflexive verb form meaning "will begin/start," with reference to a planned event (the meeting).