lollapalooza - something extraordinarily impressive, similar to a humdinger.
Attested from the 1890s but the origin is unknown; it could be a made-up word. New to me, it was in a book I’m reading. Though I’d never seen it before, the context made it clear at once what it meant, and I’ve learned a new word. Language is so productive, it’s possible to invent words that speakers will instantly grasp and start using.