Pneumonoultramicroscopicsilicovolcanoconiosis. Supposedly a lung infection caused by inhaling very fine volcano dust. Technically invented by a group of word puzzle fans, but it’s appeared in dictionaries.
This might also be the first time since I learned it (30+ years ago) that it’s been even close to relevant in a conversation.
FYI you can trim 80% of that. https://www.amazon.com/LEXiBOOK-Educational-Activities-Mathematics-Dactylography/dp/B0B6HKB3JF/ Amazon sure loves its tracking data.