The word gainfulness 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: 20
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (37 words)
engulfs, ensigns, ensuing, finagle, finales, finless, flanges, fueling, fungals, funnels, funnies, fussing, gainful, genials, guanine, guineas, gunless, infuses, inulase, leafing, leaning, leasing, lensing, ligases, salines, sealing, sensing, sensual, siennas, signals, silanes, singles, sunnies, unagile, unalign, unseals, unsling