Facts about words

The longest English word, at 45 letters, is 'pneumonoultramicroscopicsilicovolcanoconiosis'.

According to the Oxford English Dictionary, pneumonoultramicroscopicsilicovolcanoconiosis is a factitious word alleged to mean a lung disease 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.

This word was invented in 1935 by Everett M. Smith, president of the National Puzzlers' League, at its annual meeting. The word figured in the headline for an article published by the New York Herald Tribune on February 23, 1935, titled "Puzzlers Open 103d Session Here by Recognizing 45-Letter Word":

Pneumonoultramicroscopicsilicovolcanoconiosis succeeded electrophotomicrographically as the longest word in the English language recognized by the National Puzzlers' League at the opening session of the organization's 103rd semi-annual meeting held yesterday at the Hotel New Yorker. The puzzlers explained that the forty-five-letter word is the name of a special form of silicosis caused by ultra-microscopic particles of silica volcanic dust...

Subsequently, the word was used in a puzzle book, Bedside Manna, after which members of the NPL campaigned to have it included in major dictionaries. This 45-letter word, referred to as P45, first appeared in the 1939 supplement to the Merriam-Webster New International Dictionary, Second Edition.

'Hippopotomonstrosesquippedaliophobia' is the fear of long words.

Hippopoto- "big" due to its allusion to the Greek-derived word hippopotamus (though this is derived as hippo- "horse" compounded with potam-os "river", so originally meaning "river horse"; according to the Oxford English, "hippopotamine" has been construed as large since 1847, so this coinage is reasonable); -monstr- is from Latin words meaning "monstrous", -o- is a noun-compounding vowel; -sesquipedali- comes from "sesquipedalian" meaning a long word (literally "a foot and a half long" in Latin), -o- is a noun-compounding vowel, and -phobia means "fear". Note: This was mentioned on the first episode of Brainiac Series Five as one of Tickle's Teasers. 

Obviously it is not fear of hippos.

source: wikipedia