The word mendacious 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: 19
Highest Scoring Words With Friends™ Play In The Letters mendacious
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Seven Letter Word Alert: (36 words)
acnodes, acumens, adonise, amidone, amnesic, animose, anodise, caesium, candies, cinemas, consume, daemons, deacons, decuman, demonic, dimuons, domains, icedams, icemans, incased, incomes, induces, maidens, masonic, medians, miscode, miscued, misdone, mucoids, mucosae, muscoid, muscone, nomadic, sideman, unaimed, uncased