der Aufbruch
departure
The beginning of a journey or the act of leaving a place.
Nach einem letzten Kaffee war es Zeit für den Aufbruch zum Bahnhof.
After one last coffee, it was time for the departure to the train station.

departure / new beginning
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departure
The beginning of a journey or the act of leaving a place.
Nach einem letzten Kaffee war es Zeit für den Aufbruch zum Bahnhof.
After one last coffee, it was time for the departure to the train station.

'Der Aufbruch' (departure / new beginning) comes from the verb 'aufbrechen' (to break open; to set off). The literal meaning 'to open something by force' ('eine Tür aufbrechen' — to break open a door) is transferred to other contexts: you 'bricht auf' (set off) on a journey or into a new era.
Die Wanderer brachen schon früh am Morgen auf.
The hikers set off early in the morning.
The meaning becomes clear from the context. If it is about travel, it means the start or departure. In a historical or social context, it means the beginning of a new era. In connection with crime or violence, it means forced opening.
Der Aufbruch in den Urlaub ist für morgen früh geplant.
The departure for vacation is planned for early tomorrow morning.
In the sense of 'Abreise' (departure), the phrase 'Zeit für den Aufbruch' (time to set off) is often used. It signals that you now have to get going.
Es wird dunkel, es ist Zeit für den Aufbruch.
It's getting dark; it's time to set off.
In the figurative sense, 'Aufbruch' (new beginning) is often combined into the word 'die Aufbruchstimmung' (spirit of optimism / mood of new beginnings). It describes an optimistic feeling of a fresh start in a group or society.
Nach dem politischen Wechsel herrschte im Land eine große Aufbruchstimmung.
After the political change, there was a strong spirit of optimism in the country.
start
'der Start' and 'der Aufbruch' can both mean a beginning. 'der Start' is neutral and fits many situations, for example a trip, a project, or a career. 'der Aufbruch' puts more emphasis on leaving a place or on an important new change beginning. For journeys, 'Aufbruch' often sounds a little more vivid than 'Start' because it also means setting off. In a figurative sense, 'Aufbruch' fits when a group or society wants to begin something new.

Am Bahnhof warten die Reisenden schon auf den Aufbruch in den Urlaub.
At the train station, the travelers are already waiting to set off on vacation.
Vor dem Start der Fahrt prüft Max noch einmal die Route.
Before the start of the trip, Max checks the route one more time.