This is the 15392nd most frequent Polish word.
spadnie
"Spadnie" means "will fall" in English.
Here, 'spadnie' is used to describe the decreasing of a measurable value, specifically temperature.
Jeśli będzie mroźno, temperatura spadnie poniżej zera.
If it gets frosty, the temperature will drop below zero.
In this sentence, 'spadnie' (here in plural 'spadną') refers to objects, leaves, moving downward due to gravity.
Gdy wiatr się nasili, liście spadną z drzew.
When the wind picks up, the leaves will fall from the trees.
Here, 'spadnie' expresses the possibility of downward motion of an object, specifically a branch.