The word defervescent 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: 24
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (37 words)
centers, centred, centres, crested, decenes, decrees, defects, defence, defense, descent, deserve, entered, entrees, erected, evenest, everted, feeders, fencers, fenders, fervent, fevered, needers, recedes, reested, refects, refeeds, refence, scented, scenter, seceder, secrete, severed, sneered, steered, sterned, tenders, veneers