The word arbitrariness 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: 17
Highest Scoring Words With Friends™ Plays In The Letters arbitrariness
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Seven Letter Word Alert: (68 words)
abasers, abaters, abraser, abrases, abreast, absents, abstain, airbase, airiest, antsier, arabise, arbiter, arrears, arrests, artisan, artsier, atresia, baiters, banters, barista, barites, barrens, barrier, barters, basters, bitsier, braiser, braises, brasier, breasts, brinier, errants, inertia, inserts, instars, irisate, narrate, nastier, rainier, raisers, raisins, ranters, rarebit, rasters, rebaits, restain, restirs, retains, retinas, retrain, rinsers, satires, searats, seastar, seitans, sestina, sierras, sinters, snarers, stainer, starers, stirrer, strains, tarrier, tarries, terrain, trainer, tsarina