According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 7 words with the pattern T--TI--S-. That is, nine letter words with 1st letter T and 4th letter T and 5th letter I and 8th letter S. In alphabetical order, they are:
tactilist
tartiness
tastiness
tattiness
testiness
tintiness
triticism