To waver in the mind, will, or feeling.
MISS PRISM. [Shaking her head.] I do not think that even I could produce any effect on a character that according to his own brother's admission is irretrievably weak and vacillating. Indeed I am not sure that I would desire to reclaim him. I am not in favour of this modern mania for turning bad people into good people at a moment's notice. As a man sows so let him reap.
From Oscar Wilde's The Importance of Being Earnest.