The word interregna 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: 14
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (40 words)
angrier, antigen, arenite, earning, earring, entrain, gentian, grainer, granite, grantee, granter, greaten, greater, grinner, inerter, ingrate, integer, nearing, nitrene, rangier, ranting, reagent, rearing, regnant, regrant, regrate, reigner, reinter, renting, retrain, tangier, tarring, tearier, tearing, terrain, terrane, trainee, trainer, treeing, triaene