It's 189,819 letters long and takes more than three hours to say, but is this the world's longest word?
Methionylthreonylthreonylglutaminylarginyl…isoleucine is the chemical name of Titan, the world's largest protein, according to Geekologie.com.
A Russian man recently recorded a video of himself pronouncing the word. Sitting at a desk next to a potted flower, he spends three hours and 33 minutes reciting the entire mouthful.
But although Methionylthreonylthreonylglutaminylarginyl…isoleucine qualifies as the longest word in English, don't expect to find it in the dictionary.
Because it's a technical term for a chemical, it won't appear there.
In fact, some lexicographers aren't sure whether the name of a chemical actually qualifies as a word, and are dubious of its world's longest word status, according to The Huffington Post.
One thing's for sure. It is a mouthful.