die Ewigkeit
eternity
A state or period of time without beginning and without end; infinite duration.
Manche Religionen lehren, dass die Seele für die Ewigkeit weiterlebt.
Some religions teach that the soul lives on for eternity.

eternity
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eternity
A state or period of time without beginning and without end; infinite duration.
Manche Religionen lehren, dass die Seele für die Ewigkeit weiterlebt.
Some religions teach that the soul lives on for eternity.

'Die Ewigkeit' (eternity) is derived from the adjective 'ewig' (eternal). The ending '-keit' is a typical way to form abstract, feminine nouns from adjectives that describe a state or quality.
Manche Menschen glauben an ein ewiges Leben nach dem Tod.
Some people believe in eternal life after death.
In the philosophical or religious meaning, 'Ewigkeit' (eternity) is often used in fixed expressions such as 'für die Ewigkeit' (for eternity) or 'bis in alle Ewigkeit' (for all eternity).
Diese alten Steinbauten scheinen für die Ewigkeit gemacht zu sein.
These old stone buildings seem to have been made for eternity.
The use of 'Ewigkeit' (eternity) for a very long but limited period of time is colloquial and exaggerated. It is often used to express impatience or the length of a wait.
Der Bus hat heute Morgen eine Ewigkeit auf sich warten lassen.
The bus took ages to arrive this morning.
In the colloquial meaning, the indefinite article 'eine' (an/a) is almost always used. Typical verbs in this context are 'dauern' (to last/take) or 'warten' (to wait).
Es hat eine Ewigkeit gedauert, bis ich endlich einen Parkplatz gefunden habe.
It took ages before I finally found a parking space.
moment
'der Moment' and 'die Ewigkeit' are strong opposites when talking about time. A 'Moment' is very short or a specific brief point in time. 'Ewigkeit' means a time without end, or colloquially a very long time. If you are only supposed to wait briefly, 'Moment' fits. If something takes an extremely long time or feels that way, 'Ewigkeit' fits. So the contrast is: very short versus very long.

An der Kasse hat die Wartezeit wie eine Ewigkeit gewirkt.
At the checkout, the wait felt like an eternity.
Für einen Moment war es im ganzen Raum still.
For a moment, the whole room was silent.