Vacillate 一词源自拉丁语vacillare（来回摆动；犹豫）的过去分词vacillatus，16世纪末进入英语后也是用来表示因缺乏平衡而不稳定地“摇摆、波动、震荡”，

比如：

The earthquake caused the house built using salvaged materials to vacillate.地震使这座用回收的废旧材料建成的房屋摇来晃去。

Oh, do stop vacillating and make up your mind. There is no room for sentiment in business.等到了17世纪20年代后， vacillate 开始发展出现在的主要含义指观点或立场的“摇摆、动摇、犹豫、踌躇”，常意味着因无法作出固定不变的或最终的决定而导致长时间的犹豫，诸如在不同的意见、选择或效忠对象之间来回摇摆或不停转变，比如：哎哟，别再犹豫了，打定主意吧！做生意不能感情用事。

The volatile actress was affable at one moment, choleric the next. Her mood vacillated between hope and despair.这位情绪无常的女演员一会儿还和蔼可亲，可一转眼就火冒三丈。她时而心怀希望，时而感到绝望。

At the meeting celebrating the 20th anniversary of Hong Kong's return to the motherland in 2017, I stated that the central government, in implementing the principle of "one country, two systems," will maintain two key points: first, the central government will remain resolute in implementing the principle, and will not change or vacillate in this stand; and second, the principle will be implemented as what it is originally intended precisely.权威用例在庆祝香港回归祖国20周年大会上，我曾经讲过，中央贯彻“一国两制”方针坚持两点，一是坚定不移，确保不会变、不动摇；二是全面准确，确保不走样、不变形。

出自习主席在庆祝香港回归祖国25周年大会暨香港特别行政区第六届政府就职典礼上的讲话（双语全文）

dither: be indecisive teeter: be unable to decide between different courses; waver oscillate: waver between extreme同近义词