German words ending in -chen

This is the ending that overrides the others. -chen is the diminutive: it makes a small or affectionate version of a noun, and it resets the gender to neuter on the way through. Der Hund gives das Hündchen. Die Blume gives das Blümchen. Das Brot gives das Brötchen. Whatever article the original had is discarded, not weighed against anything.

Which answers the question every learner asks. Why is das Mädchen neuter when it means girl? Because Mädchen is a diminutive, built on the old word Magd, and -chen took the gender the moment it attached. The grammar is describing the shape of the word, not making a claim about the person. -lein does exactly the same thing, which is why Fräulein is also das.

The stem often takes an umlaut when the ending goes on: Brot to Brötchen, Hahn to Hähnchen, Hund to Hündchen. That is a useful signal in reverse, because it helps you find the word underneath.

All of this holds only where -chen is genuinely the suffix. Kuchen and Knochen end in those letters and are not the small version of anything; there is no Kuch and no Knoch for them to be built on. The test is to remove the ending and see whether a word is left. And some nouns end this way for reasons of their own: das Zeichen is an old noun in its own right, old enough that the verb zeichnen was built from it rather than the other way round. It is not a diminutive at all, it simply lands on the same article by another route.