What everyday word from the English language uses the highest number of differing letters? I am after the shortest word with the most letters.

eg.
KNIFE has 5, where SPOON only has 4. so KNIFE is better.
The word SPINES has 5 differing letters but is 6 letters long so KNIFE would be better here also.
The word POSTERS has 6 differing letters, even though it is 7 letters long, this will beat KNIFE.