The word cirrostratus 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: 16
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (27 words)
artists, autists, carrots, castors, citator, corsair, costars, cuatros, curator, cursors, outcast, outsits, racists, ricotta, rustics, scorias, statics, straits, stratus, suitors, taoists, tourist, tractor, traitor, tricots, trocars, tsarist