The word posteriority 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: 17
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (39 words)
isotope, isotype, pietist, pitiers, poorest, porters, potters, pottery, potties, presort, protest, protist, pyrites, reports, reroots, retorts, rioters, risotto, roister, rooster, rooters, ropiest, rotters, sootier, spotter, stipite, stooper, striper, stripey, tipsier, tipster, tiptoer, tiptoes, tooters, tootsie, torpors, trooper, tropist, tryster