The word marrowbones 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 marrowbones
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Seven Letter Word Alert: (29 words)
anomers, barrens, barroom, barrows, bemoans, beswarm, boomers, boranes, borrows, browner, browser, enamors, maroons, marrows, moaners, narrows, oarsmen, reswarm, rewarms, roamers, roomers, searoom, seaworm, seaworn, swarmer, swooner, warmers, warners, wormers