The word covariances 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: 22
Highest Scoring Words With Friends™ Play In The Letters covariances
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Seven Letter Word Alert: (33 words)
arcsine, arsenic, avarice, cancers, canoers, carinae, carnies, carvone, caverns, coarsen, cocaine, coiners, concave, concise, corneas, cornice, covines, cronies, evasion, novices, oceanic, ovarian, ovaries, ravines, recoins, rosacea, scoriac, scoriae, vaccine, varices, version, viscera, voicers