What is the longest non-medical word in the English language?

While there are a number of candidates depending on what scientific names/words are allowed, floccinaucinihilipilification is the most uncontroversial choice.

"The Guinness Book of Records, in its 1992 and subsequent editions, declared the "longest real word" in the English language to be floccinaucinihilipilification at 29 letters.

Pneumonoultramicroscopicsilicovolcanoconiosis also appeared in the Oxford dictionary, but the actual medical name of this disease is pneumoconiosis, leaving it controversial because it may have been made up by Everett Smith.

Wiki calls floccinaucinihilipilification "the longest unchallenged nontechnical word".

https://en.wikipedia.org/wiki/Longest_word_in_the_English_language

Pneumonoultramicroscopicsilicovolcanoconiosis is longer, according to the book of records.

Pneumonoultramicroscopicsilicovolcanokoniosis is, according to the Oxford English Dictionary, "a factitious word alleged to mean 'a lung disease caused by the inhalation of very fine silica dust causing inflammation in the lungs. Occurring chiefly as an instance of a very long word." It was coined to serve as the longest English word and is the longest word ever to appear in an English language dictionary. This 45-letter word, referred to as P45, first appeared in the 1939 supplement to the Merriam-Webster New International Dictionary, Second Edition. It is listed in the current edition of several dictionaries. A condition meeting the word's definition is normally called silicosis.

https://en.wikipedia.org/wiki/Pneumonoultramicroscopicsilicovolcanoconiosis

I once had to say the word "honorificabilitudinitatibus" in a play, Shakespeare's "Love's Labour's Lost."

https://en.wikipedia.org/wiki/Honorificabilitudinitatibus
http://www.worldwidewords.org/weirdwords/ww-hon1.htm

The longest word in any major English language dictionary is pneumono­ultra­micro­scopic­silico­volcano­coniosis, a 45-letter word supposed to refer to a lung disease, but research has discovered that this word was originally intended as a hoax. It has since been used in a close approximation of its originally intended meaning, lending at least some degree of validity to its claim. The Oxford English Dictionary contains pseudopseudohypoparathyroidism (30 letters).

The longest non-technical word is flocci­nauci­nihili­pili­fication at 29 letters. Consisting of a series of Latin words meaning "nothing" and defined as "the act of estimating something as worthless," its usage has been recorded as far back as 1741.[2][3][4] In recent times its usage has been recorded in the proceedings of the United States Senate by Senator Robert Byrd [5], and at the White House by Bill Clinton's press secretary Mike McCurry, albeit sarcastically.[6]

Anti­dis­establishment­arianism (a nineteenth century movement in England opposed to the separation of church and state) at 28 letters is still in colloquial currency for being one of the longest words in the English language.

answers.com/longest%20word%20in%20the%20English%20language no longer exists

Floccinaucinihilipilification
-the act or habit of estimating or describing something as worthless

http://dictionary.reference.com/browse/Floccinaucinihilipilification
and https://en.wikipedia.org/wiki/Floccinaucinihilipilification

The longest word in English is PNEUMONO­ULTRA­MICRO­SCOPIC­SILICO­VOLCANO­CONIOSIS (also spelled PNEUMONO­ULTRA­MICRO­SCOPIC­SILICO­VOLCANO­KONIOSIS) which are all 45 letters long!
On this site you will find the definition too.
http://www.fun-with-words.com/word_longest.html