The word diphthongizes 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: 33
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (70 words)
deposit, dieting, dingies, dishing, dogship, dopiest, dozenth, doziest, editing, edition, eighths, ghosted, godsent, gothish, heights, hidings, highest, hightop, histone, hogtied, hogties, hoisted, hosting, ignited, ignites, indepth, indigos, indites, inosite, insight, iodines, iodites, iodizes, ionised, ionized, ionizes, iotized, iotizes, iphones, nightie, phished, phizogs, phonies, pigeons, pingoes, pithing, pointed, poising, posited, posting, seizing, shindig, shoeing, sighted, spinode, spionid, spiting, sponged, stipend, thighed, thiones, thonged, tidings, tiepins, topside, zeniths, zesting, zionist, zipties, zoisite