The word superimpose 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™ Plays In The Letters superimpose
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Seven Letter Word Alert: (50 words)
empires, empress, epimers, episome, espouse, imposer, imposes, impress, isomere, isomers, meioses, messier, misuser, moppers, mossier, mousers, mousier, oppress, peruses, poesies, poseurs, premise, premiss, pressup, presume, promise, pumpers, purpose, pussier, reissue, repipes, reposes, repumps, resumes, ruesome, serious, simpers, sippers, soirees, soppers, soppier, soupier, spumier, suppers, suppose, supreme, surmise, suspire, umpires, uprises