The word roistering 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: 13
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (30 words)
girners, goiters, goitres, goriest, grister, igniter, ignites, ignitor, ignores, inosite, ioniser, ironers, ironies, noisier, norites, orients, origins, regions, resting, ringers, rioters, rioting, roister, snorter, sorting, stinger, stonier, storing, tiering, triones