The word birefringent 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 birefringent
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Seven Letter Word Alert: (31 words)
beefing, beignet, benefit, briefer, bringer, brinier, feigner, ferrite, fierier, firring, freeing, fringer, grinner, igniter, inerter, integer, niftier, nitrene, rebegin, rebrief, reefing, refiner, reifier, reigner, reining, reinter, renting, rifting, tiering, tinnier, treeing