I Like Learning New Words

Methionylthreonylthreonylglutaminylarginyl...isoleucine' (edited) is the chemical name of 'titin' (also known as 'connectin') - the largest known protein. It has 189,819 letters.
There is a dispute as to whether it's a complete word as it is made up of other protein related words.

Apparently it took a guy 3 hours to pronounce it.

I didn't want to paste the complete word here as someone might think it was spam. Lolol.