Other forms: vacillatingly
If someone can't make up their mind, you can call that person vacillating. A vacillating student might not know whether to commit to a major in electrical engineering or in art history.
The word vacillating comes from the Latin vacillat- meaning "swayed." When you're having trouble sticking to a decision, you can be described as vacillating — meaning that you are swaying between two choices. The spelling of vacillating can be tricky to remember. But vacillating, like its definition "uncertain," has the letter c in it. And to remember the two ls, think about the word's meaning, wavering between two choices.