Pneumonoultramicroscopicsilicovolcanoconiosis

Is commonly considered to be the longest word in the english language, however the longest word is actually the scientific name for titin. Both of these words are very medical/scientific so you are unlikely to find them in a language dictionary - especially not the scientific name for titin because it is One hundred and eighty nine thousand, eight hundred and nineteen (189'819) letters long.
Pneumonoultramicroscopicsilicovolcanoconiosis is a lung disease caused by inhaling too much volcanic ash, or other rock containing similar compounds.

"The miner has been diagnosed with black lung, or pneumonoultramicroscopicsilicovolcanoconiosis"
"Wow, that's a long word"