fluctuate
FLUK-choo-aytverbMeaning to rise and fall irregularly
Memory hook FLUCT = WAVE: up and down. The little boat rides the waves up, down, up, down, never level for a moment. Things that rise and fall like waves fluctuate.
The price of strawberries fluctuates with the seasons.
In context Desert temperatures fluctuate wildly: an afternoon can top 100 degrees, and the same night can drop close to freezing.
Similar vary, rise and fall, swing, seesaw
Opposite stabilize, hold steady
From Latin fluctuare, “to move like a wave,” from fluctus, a wave.