The word undershirt 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: 15
Highest Scoring Words With Friends™ Play In The Letters undershirt
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Seven Letter Word Alert: (33 words)
dithers, druther, dunites, dustier, hinders, hirsute, hunters, hurried, hurries, hurters, insured, insurer, intrude, nutsier, returns, rudites, runtier, rustier, shirted, shrined, shunted, shunter, stirred, strider, studier, thunder, tinders, turners, turrids, undrest, uniters, untired, untried