The word unmercifulness 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: 28
Highest Scoring Words With Friends™ Play In The Letters unmercifulness
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Seven Letter Word Alert: (99 words)
celsius, censers, censure, cerises, ceriums, cerumen, cesiums, cruises, cumenes, curiums, emulsic, emulsin, ensures, felines, felsics, fencers, fennels, ferulic, fescues, finesse, finless, firemen, fissure, flenser, flenses, fuelers, fulcrum, funnels, funnier, funnies, furless, fussier, iceless, incense, infuser, infuses, insures, leisure, leucine, leucism, license, linemen, mercies, messier, mincers, minuses, miscues, misfuel, misrule, misuser, mueslis, muscles, muslins, nemesis, nucleus, numeric, recline, recluse, recuses, refiles, refilms, refines, reflies, refuels, refuses, reissue, reliefs, relines, remines, rescues, reslice, resumes, rimless, rumless, runnels, screens, secerns, secures, selfies, siemens, silence, sincere, sinners, slicers, sluicer, sluices, smilers, sulfurs, sunnier, sunnies, sunrise, surmise, uncrime, uncurls, uncurse, unfurls, unreels, unrisen, urnfuls