The word witheringly 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: 22
Highest Scoring Words With Friends™ Play In The Letters witheringly
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Seven Letter Word Alert: (28 words)
enlight, igniter, inertly, inherit, lengthy, lighten, lighter, lignite, lintier, nightie, nightly, relight, relying, retying, rightly, ringlet, tiering, tingler, weighty, welting, whinger, whinier, whitely, whiting, wilting, winglet, wintery, writing