The word "before" refers to something that happens or exists prior to a certain point in time or in relation to something else. For example, "I arrived at the restaurant before you did." It indicates a time frame or an order in which events occurred.
On the other hand, "after" indicates the opposite meaning. It refers to something that happens or exists later in time or in relation to something else. Using the same example, "I arrived at the restaurant after you did." It suggests a subsequent time frame or a different order of events.
The term "after" serves as a directional marker, depicting a shift from a previous state or moment to a consequent state or moment. It is essential in understanding the chronological order of events or actions. Thus, "after" is the correct opposite of "before".
Please note that there are other terms that can also convey the opposite meaning of "before", such as "following", "subsequent", or "later". However, "after" is the most commonly used and direct antonym for "before".