Pre-arranging refers to the act of planning or organizing something in advance. Its antonyms include spontaneous, unplanned, impromptu, extempore, off-the-cuff, and spur-of-the-moment, among others. These words convey a sense of being done without forethought or a preconceived plan. Spontaneous implies coming from natural impulse or impulse without external stimulus or constraint. Unplanned suggests an event or activity that was not anticipated or intended. Impromptu means something done on the spur of the moment with little or no preparation. Extempore refers to something done or spoken without preparation, whereas off-the-cuff suggests something done without preparation or rehearsal. Lastly, spur-of-the-moment means something done impulsively or suddenly, without premeditation.