This longest unchallenged nontechnical word
That not many directories know or have heard

Often times it's used in a humorous way
It's pronunciation is quite hard to say

Its numbers of letters, I count 29
The meaning of it I aim to define

The action or habit of something as worthless
A word it seems that serves not much purpose

An interpretation of this means "for nothing"
Found in the Eton Grammar textbook in Latin

Used by an English poet in work of his own
In 1741 by William Shenstone

Not used much today,  wonder why this is true?
This sesquipedalian has not much value!