How about this word?
One of my favorites.
indubitably
Indubitably means "without doubt." If you say that you are indubitably going to run for class president, you're sure of it.
With five syllables, indubitably is kind of a mouthful. Here's how to say it: "in-DOO-bit-a-blee." And while it is more of an old-fashioned adverb, indubitably remains a unique way to say "undoubtedly." In fact, doubt and indubitably share a root in the Latin word dubitabilis, meaning "doubtful." Adding the prefix in- makes something done indubitably without a doubt.