The word perfidiously 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: 23
Highest Scoring Words With Friends™ Play In The Letters perfidiously
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Seven Letter Word Alert: (47 words)
defouls, deploys, despoil, dipoles, direful, doilies, dropfly, elusory, euploid, fierily, floured, folders, foldups, idolise, iodiser, leprosy, leprous, liriope, lousier, oilfire, ourself, perfidy, periods, pilfers, piously, presold, profile, profuse, proudly, purfled, purfles, pylorus, reflips, refolds, slurped, soldier, soliped, soupier, spidery, spiroid, spoiled, spoiler, sporule, sulfide, syruped, upfolds, yodlers