From 16 November 1942 onwards, Anne Frank had to share her room with the dentist [Fritz Pfeffer](https://en.wikipedia.org/wiki/Fritz_Pfeffer), who had a number of habits that Anne couldn't stand. In the German biography *Anne Frank* (Reinbek bei Hamburg: Rowohlts Taschenbuch Verlag, 2002), Matthias Heyl writes:
> In ihrer überarbeiteten Tagebuchversion revanchierte [Anne Frank] sich damit, dass sie ihm den weder im Niederländischen noch im Deutschen schmeichelhaften Namen «Dussel» verpasste.
My translation:
> In the reworked version of her diary, [Anne Frank] took revenge on him by giving him the nickname "Dussel", which is unflattering, both in German and in Dutch.
(More literally translated: "flattering neither in German nor in Dutch".)
The German Wiktionary defines [Dussel](https://de.wiktionary.org/wiki/Dussel) as "ungeschickter Mensch" (awkward/inept/unintelligent person). Something similar can be found in the [online Duden dictionary](https://www.duden.de/rechtschreibung/Dussel).
But as far as I know, [dussel](https://www.vandale.nl/gratis-woordenboek/nederlands/betekenis/dussel) is not a word in Dutch (my native language). So why would the name be unflattering in Dutch? I am looking for evidence in a reliable *offline* source; I have seen too much nonsense on the Web.
Anne Frank was born in Germany and spoke German. She may have made assumptions that the insult would be understood in Dutch. In her own diary there is no description of the word Dussel as an insult.
