The word unsimilarity 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: 20
Highest Scoring Words With Friends™ Play In The Letters unsimilarity
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Seven Letter Word Alert: (27 words)
animist, atriums, initial, insular, marlins, martini, martins, militar, militia, mistily, mistral, misturn, mustily, nastily, nitryls, rituals, ruminal, rustily, saintly, similar, smartly, stimuli, trysail, tsunami, unitary, unsilty, urinals