Nastie question .

[swannbaker]

What is the longest word you can find using only the letters A E I N S T , the only requirement being that no letter must be used twice .

[cruciverbali]

Tisane

[mrkester]

tisane - An herbal infusion or similar preparation drunk as a beverage or for its mildly medicinal effect.

tenias - A narrow band or ribbon for the hair that was worn in ancient Greece.

tineas - a derivation of ringworm

OR AM I MISSING THE POINT?

[cruciverbali]

Intenseness

[cruciverbali]

Assassinates

[cruciverbali]

Insensateness

[donslot]

Sorry I don't have a direct answer to this but here's a site worth bookmarking for another rainy day...
http://www.aivazoglou.gr/10.html

[Sasha13]

Surely if no letter can be used twice, the longest word will be 6 letters long? Hence mrkester must have answered the question?

[swannbaker]

Mr k yes , you are missing the point .
ccvbl well done . I don't think you can get past 13 .

[Christiana]

In case the point is still escaping you, no letter IS used twice, it doesn't say you can't use them more than twice though.

[juliefer]

Making the noun insensateness plural gives the 15-letter word insensatenesses.

[Sasha13]

Ah, got ya. That was far too complicated for me on a Friday afternoon!