This is the 17346th most frequent Polish word.
zapadł
"Zapadł" means "fell" or "sank" in English, depending on context.
Here, "zapadł" is used to signify the occurrence or descent of darkness (zmrok).
Zapadł zmrok, gdy spacerowaliśmy przez las.
Darkness fell as we were walking through the forest.
In this sentence, "zapadło" expresses the settling or establishment of cold conditions in a place.
Zimno zapadło w domu po zepsuciu ogrzewania.
Coldness settled in the house after the heating broke down.
Here, "zapadła" is used to indicate that a decision was reached or concluded.