intr.v. vac·il·lat·ed, vac·il·lat·ing, vac·il·lates
1. To be unable to choose between different courses of action or opinions; waver: She vacillated about whether to leave.
2. To change between one state and another; fluctuate: The weather vacillated between sunny and rainy.
3. Archaic To sway from one side to the other.
[Latin vacillāre, vacillāt-, to waver.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.