The word conclusively 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™ Plays In The Letters conclusively
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Seven Letter Word Alert: (27 words)
celcius, closely, collies, collins, concise, conveys, council, counsel, covines, cyclins, cyclise, cyclone, elusion, envious, locules, lousily, novices, nucleic, occluse, ovicell, ovinely, sunlily, sylvine, unclose, uncoils, unveils, volleys