departure
The act of leaving a place or going away.
Departure means leaving or going away from a place. When your family's flight boards at the airport, you head to the departure gate. When guests say their goodbyes and leave your house, that's their departure. Saying a school bus departs at 8:00 AM means it leaves at that time.
The word also describes a change from the usual way of doing things. If your teacher normally gives written tests but suddenly announces an oral exam, that's a departure from her normal routine. When a musician tries a completely different style of music, critics might call it a bold departure from her earlier work.
Notice that departure usually suggests something intentional and noticeable. You wouldn't say walking from your bedroom to the kitchen is a departure, but moving to a new city definitely is. Similarly, small tweaks to a recipe aren't departures, but switching from baking cookies to making sushi would be.
The opposite of departure is arrival. At airports, you'll see these words everywhere: the departures board shows flights leaving, while the arrivals board shows flights coming in.