Words
das Fugen-s
In English: linking s (in compounds)
An extra s that joins the two parts of some compound words. It has no meaning and is not a plural or a genitive; it always follows first parts ending in -ung, -heit, -keit, -schaft, -ion, -tät.
Example: Wann ist dein Geburtstag? (die Geburt + s + der Tag)