The word conclusiveness 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 conclusiveness
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Seven Letter Word Alert: (65 words)
celcius, celsius, cession, ciscoes, concise, concuss, connive, consuls, convene, cosines, coulees, council, counsel, cousins, covines, elusion, elusive, enclose, enliven, ensouls, envious, evinces, evulses, iceless, incense, insoles, lesions, lessens, lessons, leucine, licence, license, lioness, nonevil, novices, nucleic, nucleon, occluse, oneness, osseins, ossicle, science, sconces, sessile, session, silence, sinless, sinuses, slovens, sluices, snivels, sonless, success, sunless, sunnies, unclose, uncoils, unveils, useless, veinule, venison, venules, vesicle, vessels, viscous