5
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What's the longest English word that doesn't contain the same two letters in a row more than once?

Good word : too contains to once and oo once.

Good word : tot contains to once and ot once.

Bad word : aardvark contains most pairs once but ar appears twice.

Handy JavaScript test function :

function test_word(w){
    for(var l=[],i=1; i<w.length; i++){
        var p=w[i-1]+w[i];
        if( l[p] ) return p;
        l[p]=true;
    }
    return true;
}

To test your word read the link above then copy and paste the test function hit enter then use the command:

test_word('yourword');

It will return true if it is good and the repeated characters otherwise.

You can also check the word in Excel by entering the word into the cell A1 and entering this formula elsewhere as an array formula using Ctrl+Shift+Enter: (It will return TRUE if it is good and FALSE if it is not.)

=MAX(LEN($A$1)-LEN(SUBSTITUTE(UPPER($A$1),MID(UPPER($A$1),ROW(OFFSET($A$1,0,0,LEN($A$1)-1)),2),"")))<=2
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  • $\begingroup$ Eurgh, programming! :-s $\endgroup$ – Rand al'Thor Jul 6 '15 at 12:19
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    $\begingroup$ Automated checking of results. Its very useful. $\endgroup$ – Bob Jul 6 '15 at 12:23
  • $\begingroup$ So the upper limit would be $325$ because ${26 \choose 2}=325$ except that the pairs can interact so the actual limit is lower. Anybody with the math skills to compute it? $\endgroup$ – Engineer Toast Jul 6 '15 at 12:29
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    $\begingroup$ How about the classic answer of smiles because there's a mile between the first and last letter? $\endgroup$ – Engineer Toast Jul 6 '15 at 12:35
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    $\begingroup$ @f'' Ah, right. Thanks. I... I don't think we'll find a valid word that long, though. $\endgroup$ – Engineer Toast Jul 6 '15 at 12:55
15
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A 22-letter word:

counterrevolutionaries!

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    $\begingroup$ This one is noteworthy for being the longest word (so far) that isn't some crazy science/medical term. $\endgroup$ – Kevin Jul 6 '15 at 12:53
  • $\begingroup$ @Kevin And indeed the only one other than my "incomprehensibility" and some of Demesne's shorter words! $\endgroup$ – Rand al'Thor Jul 6 '15 at 12:55
8
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A 27-letter word:

psychoneuroendocrinological

A 26-letter word:

radioimmunoelectrophoresis

A 25-letter word, thanks to Kevin:

immunoelectrophoretically

And now for some words that are shorter than 20 letters, but are still pretty good.

An 18 letter-word:

Arachibutyrophobia (a fear of peanut butter sticking to the roof of one's mouth) - wonder if anyone really suffers from this one..

A 17-letter word:

Quattuordecillion (a cardinal number represented by 1 followed by 45 zeros)

Two 16-letter words:

Slubberdegullion (A filthy, slobbering person); hypervitaminosis (refers to a condition of abnormally high storage levels of vitamins)

A 14-letter word:

phantasmagoria - a sequence of real or imaginary images like those seen in a dream.

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  • $\begingroup$ Fan-tastic! But shouldn't it be "phantasmagoria", which is only 14 letters? I've never seen "phanstasmagoria". $\endgroup$ – Rand al'Thor Jul 6 '15 at 12:51
  • $\begingroup$ @rand Oops, thanks for pointing that out. A typo, my bad. Changed. $\endgroup$ – Demesne Jul 6 '15 at 12:54
5
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First candidate:

incomprehensibility (19 letters).

Anything longer than that will probably be one of those 'silly' super-long words like floccinaucinihilipification or supercalifragilisticexpialidocious (neither of which work, by the way).

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  • $\begingroup$ good tagging edits! $\endgroup$ – Bob Jul 6 '15 at 12:01
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    $\begingroup$ What's wrong with floccinaucinihilipilification?! (And why doesn't my phone keypad have an interrobang?!) $\endgroup$ – Ben Jul 6 '15 at 17:43
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    $\begingroup$ @Ben It has "in" twice. $\endgroup$ – Rand al'Thor Jul 6 '15 at 19:47
  • $\begingroup$ @Ben it is a rotten shame that the interrobang is not on your phone keypad nor on any standard keyboard (to my knowledge). $\endgroup$ – Conor O'Brien Jul 6 '15 at 20:34
3
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A 20-letter word:

electroencephalogram

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3
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How about this 25 letter word:

immunoelectrophoretically

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    $\begingroup$ NB. I picked this out of the Words With Friends word list. I wonder why it's in there when it can't fit on the board. $\endgroup$ – Kevin Jul 6 '15 at 12:28
  • $\begingroup$ Interesting that they didn't even bother removing words of length 17+. Bit of a silly choice, isn't it? Out of curiosity, how did you get access to that word list? $\endgroup$ – Curmudgeon Jul 6 '15 at 12:43
  • $\begingroup$ Unfortunately, I have forgotten how I originally came upon this list. You can download the ENABLE word list, which the WWF list is based on, but it's missing the additions the devs made, like "zen" and "texting". $\endgroup$ – Kevin Jul 6 '15 at 12:52
2
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Building off of this answer

24 letters

intercomprehensibilities

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2
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A 20-letter word!:

uncharacteristically

And another 22-letter word: deinstitutionalization (Sorry, I messed up on the program. Here is the revised):

def test(w):
    l = set()
    for i in range(1,len(w)):
        p = w[i-1]+w[i]
        l2 = l&l
        l.add(p)
        if l2==l:
            return False
    return True

Here is the code I used to look through a massive amount of words:

f = open("5desk.txt","r") # best match: 5desk.txt

longest = ""

for line in f:
    lt = test(line)
    line = line.replace("=","").replace("^","").replace("+","").replace("#","")
    if(lt):
        #print(line,len(line))
        if(len(line)>=len(longest) and not (line.find(" ")+1) and not (line.find(",")+1)):
            longest = line
            print(line,len(line)-1)

print("done.")
input("")

And here is the amalgamated input, proving that rand al'thor has the longest recognized word in my lists:

2+2GFREQ.txt
============
the
 3
and
 3
for
 3
that
 4
this
 4
from
 4
have
 4
with
 4
your
 4
about
 5
information
 11
application
 11
description
 11
development
 11
association
 11
communication
 13
accommodation
 13
administration
 14
recommendation
 14
transportation
 14
administrative
 14
characteristic
 14
implementation
 14
infrastructure
 14
classification
 14
discrimination
 14
interpretation
 14
organizational
 14
pharmaceutical
 14
rehabilitation
 14
telecommunication
 17
commercialization
 17
multidisciplinary
 17
industrialization
 17
interrelationship
 17
superconductivity
 17
videoconferencing
 17
counterproductive
 17
electrocardiogram
 17
misinterpretation
 17
counterinsurgency
 17
decriminalization
 17
electrocardiography
 19
compartmentalization
 20
counterrevolutionary
 20
electroencephalogram
 20
2+2LEMMA.txt
============
compartmentalization
 20
counterrevolutionary
 20
electroencephalogram
 20
2OF4BRIF.txt
============
electroencephalogram
 20
electroencephalograms
 21
2OF12.txt
=========
meter-kilogram-second
 21
2OF12INF.txt
============
compartmentalizations
 21
counterrevolutionaries
 22
3ESL.txt
========
5DESK.txt
=========
6OF12.txt
=========
AGID.txt
========
NEOL2007.txt
============
done.

So until I find another list of words, I believe rand al'thor has the longest word. (Though, on the bright side, I have a nice, long list of runner-ups :P)

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  • 1
    $\begingroup$ Nice summary. +1, even though I usually don't like programming answers :-) $\endgroup$ – Rand al'Thor Jul 7 '15 at 17:23
2
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Not the longest one, but I think it deserves a mention in a question like this :)
At 18 letters...

sesquipedalianisms - The practice of using long, sometimes obscure, words in speech or writing

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