The word birefringences 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: 27
Highest Scoring Words With Friends™ Play In The Letters birefringences
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Seven Letter Word Alert: (62 words)
beefier, beefing, berries, besiege, bingers, briefer, bringer, brinier, cringer, cringes, engines, feesing, feigner, fencers, fencing, ferries, fibrise, fiercer, fierier, fingers, finings, firings, firring, freebie, freeing, fringer, fringes, frisbee, generic, girners, greener, greisen, grinner, iceberg, incense, irenics, rebegin, rebrief, reefers, reefier, reefing, refence, refiner, refines, refires, refries, regreen, reicing, reifier, reifies, reigner, reining, reneger, reneges, rerinse, ringers, rinsing, scriber, serener, sericin, sincere, sneerer