The word slipcovers 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: 21
Highest Scoring Words With Friends™ Play In The Letters slipcovers
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Seven Letter Word Alert: (25 words)
closers, clovers, copiers, corpses, cresols, lispers, lossier, ossicle, plosive, plovers, polices, process, reclips, recoils, resoils, silvers, slicers, slivers, slopers, solvers, spicers, splicer, splices, spoiler, voicers