I found this word in a wonderful little book called The Lexicon, by William F. Buckley Jr. I skim through it occasionally, looking for new words that I might introduce to my own vocabulary as well as my WIP. Upon doing so, I discovered one very important thing. If there is wine involved, never ever use this word in a sentence. Better yet, just don't use this word in a sentence, period.
If, however, you're feeling geekish (like me most of the time). The word is hemidemisemiquaver, and it means thoughts or frustrations lasting for only passing seconds. It also means a sixty fourth note in music but the word is generally only used by the British. We Americans just call it the sixty fourth note. Go figure. I know you stand enlightened. You're welcome.