The word restfulness 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™ Play In The Letters restfulness
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Seven Letter Word Alert: (41 words)
eluents, ensures, festers, fetuses, flenser, flenses, fluents, fluster, fluters, fuelers, furless, fussers, lessens, lusters, nesters, nestles, netless, neuters, refuels, refuses, refutes, relents, renests, resents, restful, results, retunes, russets, rustles, sunless, sunsets, sutlers, tenures, treeful, tresses, trusses, tussles, unreels, unreset, unrests, useless