The word existentialists 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: 24
Highest Scoring Words With Friends™ Play In The Letters existentialists
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Seven Letter Word Alert: (80 words)
assents, attelet, attests, axinite, easiest, elastin, elitist, elixate, enlists, enseals, entails, entitle, estates, exilian, extents, ileitis, initial, insists, instate, lassies, lateens, latents, latites, laxists, laxness, leanest, lenites, lessens, liaises, lineate, listens, nailset, neatest, nestles, netless, nettles, salient, salines, sateens, seitans, seitens, senates, sensate, sessile, sestets, sestina, sestine, settles, sexiest, sexists, sexless, sextain, sextant, sextets, sextile, siestas, silanes, silents, sinless, sixteen, sixties, stalest, statins, statist, talents, tassels, tattles, taxless, tealess, teasels, telnets, tensest, tensile, testate, textile, tieless, tiniest, tinsels, titlist, tsetses