The word fastidiousness 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: 20
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (80 words)
adonise, anodise, assents, assists, astound, aunties, daisies, defiant, desists, destain, detains, dissent, donates, dunites, edition, fadeins, fadeout, fainted, fanouts, fastens, fatness, faunist, fiestas, fission, fitness, foisted, fondest, fondues, fusions, fustian, indites, infests, infused, infuses, inosite, insides, insists, instead, iodines, iodises, iodites, ionised, ionises, nosiest, nudists, osseins, outfind, outside, sadists, sadness, sainted, seasons, seitans, session, sestina, siestas, sinoids, sinuate, sinuses, sissies, snafued, snidest, snouted, softens, softies, stained, studies, studios, sudates, sundaes, sunsets, sustain, tedious, tissued, tissues, unified, unifies, unities, unsated, unseats