Is »die Neunziger« used to express the decade? Why does Duden not say so?

Question

I came across this sentence:

Ich war Ende der Neunziger nach New York gekommen.

I get here »Ende der Neunziger« means the end of nineties, however, according to Duden, the noun Neunziger means:

Mann von neunzig Jahren

How come in my example the word Neunziger not only has a different meaning, but also becomes a feminine word?

An additional question, how to express decade in general?

Answer 1

der Neunziger, die Neunzigerin

this is a person who is 90 years old. If it is a male person you use the male form »der Neunziger«, if female, then it is »die Neunzigerin«

Nom: Der Neunziger feiert seinen Geburtstag. Die Neunzigerin feiert ihren Geburtstag.
Gen: Dort steht die Torte des Neunzigers. Dort steht die Torte der Neunzigerin.
Dat: Gebt dem Neunziger seine Geschenke! Gebt der Neunzigerin ihre Geschenke!
Akk: Wir haben den Neunziger gesehen. Wir haben die Neunzigerin gesehen.

As you might have noticed, all this examples was singular. When it comes to Plural, you have:

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die Neunziger

This can be:

• more than one person being 90 years old.
• the last decade within a century (in most cases 1990-1999, but might also be 1790-1799 or 590-599 depending on the context)

(Be aware, that for the usage as decade you have to define, that the first year of a century is that one who's last digits are »00«. Then a decade is a set of years, who's digits other than the last digit are all equal.)

Persons

Nom: Die Neunziger feiern ihre Geburtstage.
Gen: Dort stehen die Torten der Neunziger.
Dat: Gebt den Neunzigern ihre Geschenke!
Akk: Wir haben die Neunziger gesehen.

Decade

Nom: Die Neunziger waren eine wilde Zeit.
Gen: Laura und Jan sind Kinder der Neunziger.
Dat: Schenkt den Neunzigern mehr Aufmerksamkeit!
Akk: Wir haben die Neunziger erlebt.

Note, that »die Neunziger« is plural (without defined gender), while »der Neunziger« is singluar and male, and »die Neunzigerin« is singular and female.
Never mix up plural number and female gender!

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die neunziger Jahre

Here »neunziger« is an adjective, describing a property of »Jahre« (years). With »die neunziger Jahre« you man the same decade of years as with »die Neunziger«. In fact, »die Neunziger« is derived from »die neunziger Jahre« by the same mechanism as in those examples:

Mein großer Sohn -> mein Großer
die neue Kollegin -> die Neue
der junge Mann/Knabe/Gesell -> der Junge

The Mechanism is called »Substantivierung eines attributiven Adjektivs« (nominalization of attributive adjectives):

An adjective is used »attributiv« (as an attribute) when it stands between an article or pronoun and a noun. In this case the adjective is an attribute of that noun, and it must be declined together with the noun. If you perform a nominalization of that attribute, you leave out the noun. So you only have left the article or pronoun and the former adjective/attribute. But now, without the noun, the former attribute turns into a noun itself. This means: Like all nouns, it has to be written with an uppercase first letter.

In some cases (»der Junge«) this nominalization is so widespread and often used, that it did become an independently noun, that in modern German is no longer thought to be a nominalization of an adjective. This is why you can find the noun »der Junge« in every dictionary.

But in most cases (»die Neunziger, mein Großer, die Neue«), when you use this words, you still have in mind, that you use an adjective in a nouns suit. And this is why you won't find such words in dictionaries as nouns, but as adjectives, which makes a big difference in German, since nouns are always written with an uppercase first letter, while adjectives (and all other words) are written with all lowercase letter (as long as they are not the first word in a sentence, at the beginning of a heading or similar cases).

But pay attention:

Die siebziger Jahre waren wirklich verrückt. Dagegen waren die neunziger geradezu brav.

Here you don't use »neunziger« as a noun. Here it is an adjective. It even is an attributive adjective! But where is the noun that should come after the attribute? It is in the sentence before, it is »Jahre«. You could also write:

Die siebziger Jahre waren wirklich verrückt. Dagegen waren die neunziger Jahre geradezu brav.

This is grammatically correct, but it is not the best style because you are repeating words. In this case you can leave out one of the »Jahre«, but since both attributes (siebziger, neunziger) still refer to an existing noun, they keep being adjectives.

You also could do this:

Die siebziger waren wirklich verrückt. Dagegen waren die neunziger Jahre geradezu brav.

Now the attribute in the first sentence has a remote noun. It is in this example in the following sentence, but that doesn't matter. It is there, so »siebziger« stays an adjective.

But watch out:

Die Siebziger waren wirklich verrückt. Dagegen waren die Neunziger geradezu brav.

No »Jahre« anywhere. So here both adjectives have to be nominalized.

Answer 2

OK, while Jan's answer is not wrong, it is a bit confusing, so I'm going to add to this just for the sake of completeness.

Neunziger can indeed mean

• A man in his nineties, which you can also put as ein Mann in den Neunzigern, which you should not confuse with:
• The decade between 1990 and 1999

In the second meaning it is a short form for die neunziger Jahre, that's why it is die Neunziger. There is also no singular form, as it always refers to more than one year, thus the declension is always the same as for all neuter plural words:

Nom: die Neunziger
Gen: der Neunziger
Dat: den Neunzigern
Akk: die Neunziger

You can - as Jan said - use this for any decade.

Answer 3

The noun Neunziger does indeed mean a man aged ninety to one hundred years. However, in your example you are dealing with the adjective neunziger which is not identical. According to Duden, it can mean:

1. (umgangssprachlich) die Zahl, die Nummer, das Jahr, den Wert neunzig betreffend
2. • das die Jahre 90 bis 99 umfassende Jahrzehnt eines bestimmten Jahrhunderts betreffend
   • das zwischen neunzigstem und hundertstem Geburtstag liegende Jahrzehnt betreffend

The meaning 2a is the one in question here. The original adjective has been implicitly placed before the noun Jahre, acquired its plural numerus (and neuter genus, but that is irrelevant), and finally nominalised to take said noun’s place.

Note that meaning 2b also includes an age of 90 to 100 — however in adjectival usage. The noun usage you found is distinct enough to warrant an own entry.

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To generally express decades, just follow the same pattern — although there is no fully established term for the first ten years of a century. Your words are:

Zehner
Zwanziger
Dreißiger
Vierziger
Fünfziger
Sechziger
Siebziger
Achtziger
Neunziger

The term nuller Jahre has gained some popularity, but I wouldn’t be sure whether it is considered ‘established’.