The word cosignatory 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 cosignatory
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Seven Letter Word Alert: (47 words)
actions, agnosic, agonist, atonics, cantors, carting, cartons, cartoon, casting, cations, citrons, coating, consort, coronas, costing, crating, cratons, crayons, cryings, gastric, gastrin, gnostic, isogony, octagon, orating, oration, organic, racoons, ratings, rations, rooting, scaring, scoring, scrying, signora, soaring, sooting, sorting, staring, staying, storing, stringy, stygian, syringa, torsion, tracing, tycoons