The concept of "being subsequent to" implies a following action or event. Antonyms for this phrase could include "preceding," which means something occurring before, or "simultaneous," which refers to two or more actions happening at the same time. Other antonyms could be "coincidental," meaning by chance, or "unrelated," indicating no connection or association between two events. Another antonym for "subsequent" could be "earlier," suggesting something that takes place prior to a particular event or period. In summary, while "being subsequent to" implies a follow-up action, its antonyms describe either something that happened before, together, or without connection to a given event.