The word horsepowers 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: 19
Highest Scoring Words With Friends™ Play In The Letters horsepowers
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Seven Letter Word Alert: (20 words)
poroses, preshow, presser, prowess, reposer, reposes, repower, repress, reshoes, reshore, reshows, resorps, reswore, showers, sorrows, spewers, spheres, swooper, whoopee, whooper