Resultantly can be defined as a word indicating that something happened due to a specific cause. Antonyms of resultantly could be any word that shows the opposite of a cause and effect relationship, such as randomly, coincidentally, accidentally, or haphazardly. These words indicate that events occurred without a direct cause, and that they were not predictable or planned. Alternatively, words such as deliberately, intentionally, or purposefully, could also be antonyms of resultantly as they indicate that something happened due to a conscious decision or action, rather than as a result of a cause and effect relationship. Overall, resultantly has several antonyms that can be used depending on the context and the desired meaning.