The german dictionary (Duden) offers an API with a free version (Duden-API - Rechtschreibprüfung-API). There already is an Urban Dictionary extension and I wondered whether someone could make one with the german dictionary, so typing !duden [Word] would give a definition in chat.
The documentation for the Duden API only indicates that it offers APIs for spellchecking and synonyms, not definitions.
There are other dictionary API vendors, however. Wictionary, for example. E.g., https://en.wiktionary.org/api/rest_v1/page/definition/anmelden , which does not require an account for authentication keys, and is fairly simple to use. However, its API only returns English results (it will define words in other languages, but the definitions are in English) Is there a particular reason to prefer one vendor over another?
Many dictionary APIs return multiple or lengthy definitions for a word. Do you have a preference for how you would want such results displayed in chat? From my experience with dictionary APIs, the first definition is not always the most common.