The German "sonder" referred to in this branch of the conversation (i.e. meaning special) is not a word on its own but a prefix for other words [0] (remember that germans like to build words from multiple separate parts and words).

While "sonder" itself is a word, it means something different when used on its own (without) [1].

0: https://www.duden.de/rechtschreibung/Sonder_ 1: https://www.duden.de/rechtschreibung/sonder