The word infidelities 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: 18
Highest Scoring Words With Friends™ Play In The Letters infidelities
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Seven Letter Word Alert: (27 words)
defiles, defines, deifies, deities, delints, dentils, destine, dieties, dietine, edifies, eleidin, felines, felsite, fileted, flensed, ileitis, indites, infidel, infield, lefties, lenited, lenites, linseed, nestled, sidelit, stifled, tensile