The word prototherian 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: 18
Highest Scoring Words With Friends™ Plays In The Letters prototherian
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Seven Letter Word Alert: (52 words)
airport, another, attirer, hairnet, harpoon, heparin, hoarier, honorer, hornier, nattier, nitrate, norther, notator, operant, oration, ornater, otarine, painter, panther, partner, patient, patriot, pattern, pertain, phonier, pointer, portent, portion, praetor, printer, pronate, prorate, protean, protein, rattier, rattoon, rehonor, repaint, repoint, reprint, retrain, rotator, taproot, terrain, thorite, tiptoer, tornote, torrent, trainer, traitor, triptan, trooper