I just use the Collins dictionary which is the best one IMO through Tor. There's no private (good) dictionary.
Edit: Also, installing an app for everything is not great for privacy either. They have a greater access to your device than a web. And for something I can perform in a web search, that's my preferred method.
It's just getting used to it. You can add the Collins (or any other dictionary search to Firefox) and it's as easy as selecting the correct search engine and writing the word in the search box.
there was an app for Wiktionary on fdroid. But I don't like Wiktionary's definitions as much as Collins'.
Friendly looks promising from things I've read and stuff but I don't know whether that would be acceptable within the App vs Browser dichotomy as "browsers" are also technically apps and Friendly is really straddling that line