The word assertiveness 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: 18
Highest Scoring Words With Friends™ Play In The Letters assertiveness
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Seven Letter Word Alert: (72 words)
aeriest, antsier, arenite, assents, asserts, assists, earnest, easiest, eastern, eeriest, ensears, entrees, entries, enviers, evenest, inserts, instars, inverse, inverts, invests, naivest, nastier, natives, nearest, nesters, ravines, renests, resaves, reseats, resents, resists, restain, restive, retains, retinas, revises, sassier, sateens, satires, seaters, seitans, seitens, senates, sensate, seriate, servant, sestina, sestine, siestas, sievert, sinters, sisters, stainer, starves, sterane, stivers, strains, striven, strives, taverns, teasers, teenier, trainee, tresses, triaene, trienes, vainest, veneers, verists, veritas, versine, veteran