Prearranging refers to planning ahead of time or making arrangements before something happens. When considering antonyms or opposites for this word, we must think about concepts that relate to spontaneity, impromptu actions and taking chances. Some antonyms for prearranging might include words like improvising, winging it, or playing it by ear. These words suggest that there is no prior planning or organization involved, and that the action or event is happening in the moment. Other antonyms could be words like flexible, adaptable, or open-ended. These concepts suggest that the situation can change and evolve as needed, and that there is no strict plan or agenda to follow.