der Eintritt
admission fee
The money you have to pay in order to enter a place (e.g. museum, cinema, swimming pool) or take part in an event.
Der Eintritt für das Konzert kostet 25 Euro.
Admission to the concert costs 25 euros.

admission / entry
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admission fee
The money you have to pay in order to enter a place (e.g. museum, cinema, swimming pool) or take part in an event.
Der Eintritt für das Konzert kostet 25 Euro.
Admission to the concert costs 25 euros.

The noun 'der Eintritt' (admission/entry) is directly derived from the separable verb 'eintreten' (to enter), which literally means 'to step in'. So 'Eintritt' is the act of going in or the result of it.
Bitte warten Sie nach dem Eintreten im Foyer.
Please wait in the foyer after entering.
When 'Eintritt' means the admission fee, it is often used with verbs such as 'kosten' (to cost), 'bezahlen' (to pay), or 'verlangen' (to charge/demand). A common and useful expression is also 'freier Eintritt' (free admission).
Wie viel kostet der Eintritt ins Museum?
How much does admission to the museum cost?
In the meaning of joining, 'Eintritt' is almost always used with the preposition 'in' followed by an accusative object. This describes which organization or group one is joining.
Sein Eintritt in den Sportverein war eine gute Entscheidung.
His joining the sports club was a good decision.
The use of 'Eintritt' for the beginning of an event, as in 'Eintritt der Dunkelheit' (onset of darkness), is typical of written language or a formal style. It often sounds poetic or official.
Bei Eintritt des Frühlings erwacht die Natur.
With the onset of spring, nature awakens.
end
'das Ende' and 'der Eintritt' are opposites when 'Eintritt' means the beginning of something. In that case, 'der Eintritt' fits the moment when a state, a period of time, or an event begins. 'das Ende' names the point at which something is over. Important: 'Eintritt' can also mean the money paid for a museum or cinema; in this contrast, however, it is not about money, but about the beginning.

Mit dem Eintritt der Dunkelheit wurde es im Wald plötzlich still.
With the onset of darkness, the forest suddenly became quiet.
Am Ende der Besprechung waren alle sehr müde.
At the end of the meeting, everyone was very tired.