subside
sub-SIDEverbMeaning to die down; also, to sink to a lower level
Memory hook SUB-SIDE: the water sinks DOWN. After the flood, the water in the park sinks down, lower and lower, until the bench appears again. The flood subsides.
After the river flooded, it took a week for the water to subside.
In context Kai’s giggles finally subsided when the teacher glanced his way, though they came right back the moment she turned to the board.
Similar abate, die down, ease, lessen
Opposite rise, increase, intensify
From Latin subsidere, “to settle down, to sink”: sub (under, down) + sidere (to settle).