The phrase "most aforethought" implies premeditation or deliberate planning. Antonyms for this phrase could include words such as spontaneous, impromptu, unplanned, or casual. These words suggest a lack of premeditation or intention, instead indicating a more relaxed approach or a situation that arises without any prior thought or preparation. Additionally, antonyms for "most aforethought" may encompass more negative connotations, such as reckless or careless, indicating a lack of consideration or forethought towards potential consequences. Ultimately, the antonyms for "most aforethought" contrast deliberate action with spontaneity or carelessness.