The word breastwork 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: 20
Highest Scoring Words With Friends™ Play In The Letters breastwork
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Seven Letter Word Alert: (20 words)
aborter, artwork, barkers, barrows, barters, bestrow, boaster, boaters, borates, brokers, browser, reboast, reroast, reworks, roaster, sorbate, starker, stroker, tarrows, workers