Etwas is not the plural of etwa

But then you hopefully knew that already! You may not, however, be completely familiar with differences between the two words and the different meanings they can have in specific contexts.

The most common translation of the pronoun etwas is "something":

Etwas hat sich schon verändert.

Something has indeed changed.

Caption 11, 2raumwohnung - Achtung fertig
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Und doch hat diese Ausstellung etwas sehr Besonderes.

However, this exhibition has something very distinct about it.

Caption 5, DDR zum Anfassen - Ganz tief im Westen
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However, when etwas is used as an adjective pronoun (usually a possessive, or noting quantities of something), it can be translated as "a bit," "somewhat," or less commonly, the simple "some":

Planktonfresser hin oder her, ihm ist doch etwas mulmig geworden,

Plankton eaters or not, he did get a bit queasy

Caption 25, Abenteuer Nordsee - Unter Riesenhaien und Tintenfischen
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Bachforellen sind etwas kleiner als die ursprünglich hier lebenden Marmoratas.

Freshwater trout are somewhat smaller than the marble trout that originally lived here.

Caption 1, Alpenseen - Kühle Schönheiten
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...verlor das Fahrrad zwischenzeitlich etwas an Bedeutung.

...the bicycle lost some of its significance for a while.

Caption 25, 200. Geburtstag - Die Geschichte des Fahrrads in 2 Minuten
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The adverb etwa can be translated as "about," "approximately" or "something like." It is most often used before a numerical measurement:

Und es sind etwa 35 Kilometer von den

And it's about 35 kilometers from the

weißen Klippen von Dover zu den Sanddünen von Calais.

white cliffs of Dover to the sand dunes of Calais.

Caption 20, Abenteuer Nordsee - Unter Riesenhaien und Tintenfischen
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Jährlich werden pro Person in Deutschland etwa 160 Liter Kaffee getrunken.

Every year, approximately 160 liters of coffee are drunk in Germany per person.

Caption 5, Eva zeigt uns - wie man Kaffee kocht
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Das bedeutet etwa „Ende des Sommers“.

That means something like "end of the summer."

Caption 6, Cettina erklärt - Halloween
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The adverb etwa can also be used as a grammatical particle, which is often difficult to directly translate, but in this case lends a suggestion of disbelief to the statement:

Rauchst du etwa wieder?

Are you smoking again?

Caption 4, 12 heißt: Ich liebe dich - Kapitel 3: Erfolgreiche Vernehmung
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Zweifelst du etwa an der Aufrichtigkeit meiner Gefühle?

Are you doubting the sincerity of my feelings?

Caption 9, Küss mich, Frosch - Die Zeiten haben sich geändert
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As you see in the two examples above, etwa is not directly translated. A more literary translation of the above examples, which gives them more of an expression of disbelief on the part of the speakers, could respectively be: "But you aren't smoking again?" and "But you aren't doubting the sincerity of my feelings?"

Further Learning
Read the definition and examples given for the particle usage of etwa on Duden, and search for etwa and etwas on Yabla German to see other examples of these words used in a real-world context.