The word faithlessness 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™ Play In The Letters
Seven Letter Word Alert: (72 words)
ashiest, ashless, assents, assists, atheise, easiest, elastin, enlists, enseals, entails, ethanes, falsest, fastens, fatness, felines, felsite, fiestas, finales, finesse, finless, fishnet, fitness, flashes, flenses, fleshes, halites, hassles, hastens, hatless, hessite, hisself, infests, inflate, inhales, lassies, lateens, leanest, leashes, lefties, lenites, lessens, lineate, listens, nailset, nestles, netless, salient, salines, sateens, sealife, seitans, seitens, selfies, selfish, senates, sensate, sessile, sestina, sestine, siestas, silanes, silents, sinless, slashes, stashes, stifles, tassels, tealess, teasels, tensile, tieless, tinsels