The word underskirt 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 underskirt
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Seven Letter Word Alert: (33 words)
diesunk, drinker, drunker, dunites, duskier, dustier, insured, insurer, intrude, kindest, knurred, nutsier, reknits, returns, rudites, runtier, rustier, skirted, stinker, stirred, strider, striker, studier, tinders, tinkers, trunked, turners, turrids, undrest, uniters, unskied, untired, untried