The word inexpressible 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 inexpressible
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Seven Letter Word Alert: (32 words)
beeline, beepers, bleeper, blesser, elixirs, expense, expires, express, inspire, lispers, peelers, penises, pieless, pinless, pissier, rebless, reexpel, relines, repeels, repiles, repines, replies, respins, ribless, risible, seepier, sleeper, snipers, spinels, spinier, spleens, splines