2. To vary in feelings, opinions, or actions from one extreme to the other: When Mildred heard the news of the accident, her reactions seemed to oscillate between hope and despair.
3. To move from above to below a mean value: The stock market seemed to oscillate around the 2500 mark.
Sometimes Mike thinks his kid sister is like a pendulum because she tends to oscillate back and forth in her opinions; for example, Lenora and her husband promised to osculate at the end of their wedding ceremony; then she started to vacillate, thinking to osculate before so many people would be embarrassing.
2. To be undecided about something; to waver between conflicting positions or courses of action: Susan appeared to be vacillating between eating a piece of chocolate cake or a piece of raspberry strudel.
3. To go back and forth in a confusing manner: It made the clerk at the library frustrated to watch Pete vacillate back and forth between which books he was going check out and which ones he would be leaving there.
4. To move or to sway in a rising and falling or wavelike pattern: The earthquake caused Christa's house to vacillate back and forth and up and down.
5. Etymology: from Latin vacillationem, "a reeling, a wavering"; from the stem of vacillare, "to sway to and fro".