Andy Nyman tweeted the following today:
Today's Fact: The word 'almost' is the longest in the English language with all the letters in alphabetical order.
— Andy Nyman (@andynyman) December 27, 2015
And because I'm an ornery sort, I wrote a script to prove it. Turns out that "almost" is one of the longest words in English to have its letters in order, but not the longest, because there are eight such words, all six letters long:
$ python src/longest-word.py abhors (6), almost (6), begins (6), biopsy (6), chimps (6), chinos (6), chintz (6), deimos (6)
You can find the code on github should you be interested.