Premeditative refers to an action or thought that has been planned or thought out in advance. However, the antonyms of premeditative are impulsive, spontaneous or unplanned. Impulsive actions are those carried out without prior thought or consideration, whereas spontaneous actions happen on the spur of the moment without any planning or forethought. Unplanned actions are those that are done immediately, without any prior knowledge or thought, and without any intention or design. These antonyms indicate that the opposite of premeditated action is impulsive, spontaneous, and unplanned reactions. Thus, premeditative is the antonym of impulsive, spontaneous, and unplanned.