Inimical comes to mind, but I'm sure there are others.
I can do you one letter better: a 7 letter word that contains three Is is "idiotic".
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aesthete
clinician
vicinities
No eight-letter words could be found in the TWL, (the Scrabble dictionary). However, these seven-letter words could be made:arenoushoarsensenhoraunhorse
Ferric: adjectiveof, relating to, or containing iron, esp. with a valence of three.