On Monday, I was asked the greatest Reference question! What is the longest word in the dictionary? While we know there are several dictionaries, the granddaddy of them all is the Oxford English Dictionary . According to that source, the loooongest word is Pneumonoultramicroscopicsilicovolcanoconiosis ! Now... what is in the world does that mean and is it even a real word? Check your local library resources or visit us at the Reference Desk to find out!