Why is it der Städter?

Städter ends in -er, and most nouns ending in -er are masculine: in a German dictionary, 86% of them take der.

All nouns ending in -er
Sense 1
der

Meaning

[1] Person who lives in a city

[1] Person, die in einer Stadt lebt

Examples

[1] My colleague was called Stetter and was a city diet

[1] Mein Kollege hieß Stetter und war Städter.

[1] "The townspeople aged and committee until they are completely sweaty in the grim cold"

[1] „Die Städter ackerten und asteten, bis sie in der grimmigen Kälte völlig durchgeschwitzt waren.“

Declension

1 Singular Plural
Nominativ der Städter die Städter
Genitiv des Städters der Städter
Dativ dem Städter den Städtern
Akkusativ den Städter die Städter

Pronunciation

Dictionary entries include material from Wiktionary. Wiktionary