The word blackwashing 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: 31
Highest Scoring Words With Friends™ Play In The Letters blackwashing
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Seven Letter Word Alert: (31 words)
abasing, awaking, backing, backsaw, balking, banksia, bashing, basking, bawling, cabling, cashing, chasing, chinwag, clawing, gawkish, hacking, hacksaw, hawking, kwachas, lacings, lacking, lashing, sacking, sawback, scaling, shaking, sickbag, walking, walkins, washing, whaling