NPR science correspondent Robert Krulwich has published a piece on the various contenders for the prestigious title of the longest word in English.
Perhaps unsurprisingly, the behemoths of the language are names given to chemical compounds, but the matter isn’t so simple. There are certain tests the word must pass: it must have been used at least once, for example, which means it needs to have been published. Most chemical compounds are referred to in annotated form, so they’re never actually printed. The longest-word-in-English title also needs to be given to a real word, not one purposely invented for the purposes of breaking records - what Krulwich refers to as a “trophy” word. Interestingly, inventing long words for the sake of it is a tradition that may stretch as far back as Shakespeare.
As for the holder of the title - well, you’ll have to read it yourself. Suffice to say, the story may have a Hollywood ending.