The word unyieldingness 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: 24
Highest Scoring Words With Friends™ Play In The Letters unyieldingness
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Seven Letter Word Alert: (77 words)
deleing, deluges, dengues, denning, densely, denying, designs, dienyne, diesels, dingies, dingily, dinning, dissing, dueling, dyeings, dyeline, dyneins, eleidin, eliding, eluding, endings, endless, engined, engines, ensigns, ensuing, eyelids, genesis, genuine, genuses, gneissy, guessed, guldens, gunless, gussied, indulge, inlines, innings, insides, insulin, inulins, issuing, legends, lending, lensing, lignins, lindens, linings, linseed, needily, needing, seedily, seeding, sending, sensing, sidings, sidling, signees, singled, singles, sinning, sledges, sliding, sludges, snidely, snudges, sudsing, sunnies, sunnily, sunning, undines, undying, unlined, unsling, yeelins, yenning, yessing