What is the longest word in the English language?

The longest word in the English language has 189,819 letters and is the chemical name for the protein, Titin. However, since it is a scientific term and not commonly used, the longest word recognized by the Oxford English Dictionary is pneumonoultramicroscopicsilicovolcanoconiosis, which has 45 letters and refers to a lung disease caused by the inhalation of very fine silica particles.