Is There a Largest Word

 When I was a young child, we were taught that the longest word was antidisestablishmentarianism. Then Mary Poppins made it Supercalifragilisticexpialidocious... 

Any long word is a sequence of bound and free morphemes.  

Mary Poppins

anti: bound, against.

dis: bound, denial.

e: bound, to make something a given quality.

stable: free, from Latin stabilire make firm.

ish: bound, having a similar quality to the noun preceding it.

ment: bound, changes verb to noun.

ari: state of belonging.

an: an individual subscribing to some point of view

ism: a distinctive doctrine or theory

Other aspects of syntax

The question of the identity of the longest word in English or any language is kinda stupid... There really is no such thing, though there are a lot of claims. The most outlandish is the recited chemical name for the protein titin. It clocks in at almost 190,000 letters...but it isn't really a word in any conventional sense. It's a list of the chemicals involved in making the protein. It would take several hours to say...and there is no reason why anyone would ever say it (other than to claim that they did). In fact, any word can be made longer. For example, if we agree that superfragilisticexpialidocious is a word, then it's meaning is nonsense. Then we can add it to the 190,000 letter word and the result would still be a word (and would still mean nonsense). That not long enough? Tack something more on to it. But, be sure to do it unantidisestablishmenterrianistically... As the next slide points out, languages differ in the degree to which the tend to form long words.