Floccinaucinihilipilification
I really had to include this one. It is – at twenty-nine letters – the longest non-technical word in the Oxford English Dictionary. I stress the “non-technical” aspect because when it comes to chemical compounds, for example, the length of a word to describe them could be effectively limitless in size. Pronounced (deep breath) flock-y-nau-chee-nee-hilly-pilly-fik-ashun, it means “the act or art of proclaiming something to be worthless”. There are several different opinions as to how it should be pronounced correctly but as it’s got (very loose) Latin roots, I’ve stuck with the Latin.
The irony of the word – as you may have noticed – is that it is in itself pretty useless as far as everyday conversation goes. It could be said to be ‘floccinaucinihilipilificatious’. If you’d spotted that this form is one letter longer than it’s nominal form, you win today’s ‘Mr or Mrs Clever Trousers’ award. This form does not appear in the OED, however – so I’ll have the prize back, thanks.
An example for illustration:
“Have you seen the new Ben Stiller movie?”
“Yes, I thought it was rubbish”
Sometimes it pays to keep things simple.

I agree, you had to include it. Abso-f*ccinaucinihilipili-lutely unbelievable.
Floccinau… *and* tmesis in one go. Bravo!
I just want to hear how long it takes to say when you’re drunk.
Bit of a moot point, really – considering anything I say when drunk is worthless. Along with many of the things I say when sober…
To be honest I only catch about 16 percent of what you say anyway as it is a load of mumbling.
I have been doing fine guess work though as you reply.
Isn’t ‘supercalifragilisticexpialidocious’ longest ? Would you dare classify ‘supercalifragilisticexpialidocious’ as technical ? Not unless forced to pretend being a muggle I suppose.
Hi David and welcome. I didn’t include it, as it is only a proper noun used to reference itself – a “meta-word”, if you like. As it has no meaning other than describe what it is, I thought it best to go for one with a clear definition.