Mammoth Uncensored Word List:
19 words ending with of, 11 letters long

bulletproof creaseproof daggerproof greaseproof insectproof mildewproof needleproof pilferproof poisonproof showerproof shrinkproof sliverproof splashproof strifeproof tamperproof terrorproof virtueproof weaponproof winterproof