The word impermissibly 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: 28
Highest Scoring Words With Friends™ Play In The Letters impermissibly
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Seven Letter Word Alert: (27 words)
biprism, imperil, implies, impress, limbers, lispers, messily, mimesis, miserly, misrely, missile, pissier, prelims, premiss, ribless, rimless, risible, similes, simmers, simpers, simpler, simples, slimier, slimmer, smilers, smileys, smilier