When talking about time in German, one word that is often found alone or as a root is das Mal. Not to be confused with das Mahl, which means "the meal," das Mal without an "h" means "the time" in the sense of "the instance." You've certainly seen sentences like this on Yabla German:
Bis zum nächsten Mal.
Till next time.
Caption 53, Abendessen: mit Marko
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There are a number of words that employ this word as a root to express a more specific relation to time. For example, einmal means "once," and so einmalig is an adjective that describes something that happens only once, or is exceptionally unique.
Diese Ansprache, die gibt es ja normalerweise nur einmal im Jahr.
This address is usually only given once a year.
Caption 3, Coronavirus: Kommentar zu Angela Merkels Rede
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Wir haben heute eine einmalige Aktion vor uns ...
We have a one-time special ahead of us today...
Caption 6, Coronavirus: Drei Musiker geben Ballonkonzert über Cloppenburg
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Ja, also wir bauen einen Baum auf, der ist drei Meter fünfzig hoch, das ist so... so einmalig.
Yes, well, we put up a tree there which is three meters fifty tall, that's so... so unique.
Captions 11-12, Weihnachten geht baden: Tannenbaum unter Wasser
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You may have also seen erstmal, which means "first," temporally speaking. If something is erstmalig, it is happening for the first time (zum ersten Mal).
Und dieser Boden ist hier in Darmstadt in der Centralstation ja erstmalig in Deutschland im Einsatz.
And this floor is here in Darmstadt in the Centralstation is in use for the first time in Germany.
Captions 1-2, Organic Disco: Tanzen gegen den Klimawandel
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Now let's look at ehemals/ehemalig and damals/damalig, which both refer to the past. You'll see these words translated in different ways on Yabla, but often with "back then," "at the time," and "former," depending on whether an adverb or adjective/adjectival phrase is required.
Es war damals irgendwie total uncool, ein Auto zu haben.
It was somehow totally uncool to have a car back then.
Caption 33, Deutsch mit Eylin: Menschen beschreiben
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Und die damalige Geschäftsführerin hat den Sender hier rübergebracht ...
And the former managing director brought the station over here...
Caption 52, Rhein-Main-TV: Interview mit Edmund Stössel
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In Pforzheim steht nach Angaben des Betreibers das einzige DDR-Museum auf ehemals westdeutschem Boden...
In Pforzheim, according to accounts of the operator, stands the only GDR museum on former West German soil...
Captions 7-8, DDR zum Anfassen Ganz tief im Westen
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Rund viertausend Besucher kommen jährlich nach Pforzheim, um etwas über die ehemalige DDR zu lernen.
Around four thousand visitors come yearly to Pforzheim to learn something about the former GDR.
Captions 39-40, DDR zum Anfassen Ganz tief im Westen
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Further Learning
Build some sentences with einmal, zweimal, dreimal, and viermal that describe how often you have been to certain places or how often you do certain tasks during the week. Then look for examples of damals, ehemals, damalig, and ehemalig translated on Yabla German to get a sense of the nuances.