word

I don't think there is technically a hardest word by definition since difficulty is determined by knowledge of the subject and natural problem solving ability. As for the longest word in the english language. Methionylthreonylthreonylglutaminlarginyl...*skipping many letters in the name*...isoleucine is the technical name for titin and is the longest word. It strings so long it contains 189,819 letters. Though there is some debate on whether it should be considered an actual word.

Pneumonoultramicroscopicsilicovolcanoconiosis.... I think it's the longest word ever appeared in Oxford dictionary in English. It's a type of disease in the lungs caused by the inhalation of very fine silica dust, causing inflammation in the lungs.'" A condition meeting the word's definition is normally called silicosis.