The word inconceivable 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: 29
Highest Scoring Words With Friends™ Play In The Letters inconceivable
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Seven Letter Word Alert: (34 words)
aclinic, albinic, aniline, anionic, avionic, biennia, binocle, bolivia, calcine, cannoli, canonic, coalbin, cocaine, coeliac, colicin, concave, conceal, conical, connive, convene, enclave, enliven, ennoble, incline, invoice, laconic, licence, nonevil, oceanic, olivine, vaccine, valence, vocable, vocalic