The word impermissible is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 26
Highest Scoring Words With Friends™ Play In The Letters impermissible
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Seven Letter Word Alert: (38 words)
bemires, beslime, biprism, blesser, emblems, empires, empress, epimers, immerse, imperil, implies, impress, limbers, lispers, members, messier, mimesis, missile, pieless, pissier, prelims, premise, premiss, rebless, repiles, replies, ribless, rimless, risible, similes, simmers, simpers, simpler, simples, slimier, slimmer, smilers, smilier