The word cassiterites 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: 15
Highest Scoring Words With Friends™ Plays In The Letters cassiterites
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Seven Letter Word Alert: (62 words)
actress, aeriest, airiest, artiest, artists, ascites, asserts, attires, casters, cattier, cerates, cerises, citrate, creases, creates, cresses, cresset, cristae, easiest, estates, iratest, irisate, iterate, raciest, racists, recasts, recites, reseats, resects, resists, restate, retaste, retests, sassier, satires, satiric, scatter, seaters, secrets, seriate, sestets, setters, siestas, sissier, sisters, sitters, staters, statice, statics, straits, streets, striate, tasters, tastier, teasers, tersest, testers, testier, tresses, trisect, tsarist, tsetses