The word silverback 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: 25
Highest Scoring Words With Friends™ Play In The Letters silverback
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Seven Letter Word Alert: (26 words)
ascribe, backers, balkers, balkier, bickers, bilkers, blacker, cablers, caliber, calibre, caviler, clavier, eclairs, lickers, rebacks, saclike, scalier, scribal, skiable, slacker, slicker, varices, velaric, verbals, vesical, viscera