The longest I could find, using both the Scrabble dictionary, and Webster's Second International, was seventeen letters:
rhomborectangular
representationalism!!!!
neurotransmitter
There's no word using all the letters, here are the longest options:routertourer
8-letter wordsoverfeed, overpaid, peroxide, prefixed
The nine letters aeohrrstw do not produce a valid English-language anagram - the longest words you can make out of these letters are the eight-letter words throwers and warhorse.
The longest word that starts with an "s" and ends with an "r" is "supercomputer."
Its the longest word that can be typed on a keyboard/typewriter and the word is "TYPEWRITER".
The longest word you can make from those letters is the word "presage". It means a foreshadowing of things to come, and it can be either a noun or a verb.
The longest word you can make out of those letters is "hydromagnetry," which has 13 letters.
The longest common word is six letters: orison.
dor, gor
Using each letter a maximum of once only, you can make the following seven-letter words from the letters "qwertyuiop": eutropy, piroque, poutier, quoiter, wipeout The longest word you can make with duplication of letters is typewriter.
Derm, err, med, red, me.