The weather vacillated between sunny and rainy.
An example of vacillate is when you pick black tiles, then white tiles, then blue tiles, then black tiles and can't make up your mind.
She vacillated about whether to leave.
Origin of vacillate
- Latin vacillāre vacillāt- to waver
From American Heritage Dictionary of the English Language, 5th Edition
- From Latin vacillÄtum, supine form of vacillÅ (“sway, waver").